Lie Detection
By Yukirei (a.k.a. Cosmiko Ling)

Characters: L, Light
Warning: Spoilers up to Page. 31, Volume 4
Disclaimer: I do not own Death Note or any of its characters. Death Note belongs to Ohba Tsugumi-sensei and Obata Takeshi-sensei, the creator and artist behind Death Note whom we should thank for bringing us such a wonderful series. This is a non-profit fanfiction written by a fan, for the enjoyment of other fans.
Summary: Light accepts L's invitation to test a newly procured lie detector. What results is a conversation of carefully worded truths - as L noses for gossip and Light assesses the best way out of the situation.
A/N: Takes place on 27 May 2004 / in Page 31, volume 4

Lie Detection is my longest Death Note fic to date (because I usually write such short ones XP). It is also the fic previously mentioned to have inspired Toothache, though I would say that while Toothache is pretty lighthearted, Lie Detection is intended to be darker.

Thanks to Shiy for having beta-read the first draft.

As this fanfiction continues from a scene in the manga, the last part of this scene (found in "Page" 31, volume 4) is quoted here for the readers' reference:

L: Yes, Light-kun isn't Kira.
If Light-kun was Kira, I would be troubled...
Because Light-kun--- is my first friend.

Light: Yes... to me, Ryuuzaki is a friend I can get along with...

L: Thanks.

Light: Since you stopped coming for class, I've been rather lonely.
I hope to play tennis with you again.

L: Yes. Certainly.
After Kira and the second Kira... No, after this whole case has been solved and Kira has been removed from this world, let's have another match.
May that day arrive soon.
Right now, not just going out, merely being seen by anyone makes me scared.
Maybe it's better if I hide...

Here on is fanfiction written by Cosmiko Ling

L's words left the room in dismal silence; the only sound remaining was the soft sipping of sugar-cube-sweetened coffee as the rest of the room's occupants wordlessly gazed upon the detective's slouched back.

Yagami-senior was the first to break the silence. Clearing his throat awkwardly, he began, "Ryuzaki..." - only to breathe a sigh when L made no response, "I'll go back to my work."

"I'll bring these latest tapes to the testing department," Aizawa followed, gathering the tapes and exiting the room after Yagami-senior.

The room returned to silence.

"I'll... I'll..." Feeling an unexplainable pressure being left alone with the two young geniuses, Matsuda scoured his mind for a task.

"Matsui-san," L spoke.

"Yes!" Matsuda snapped to attention.

"There's nothing more for you to do at the moment. Would you mind getting more of these donuts?"

"Sure! Right away!"

Matsuda left happily.

"I don't seem to have any other matters here either. If you'll excuse me, Ryuzaki, I'll take my-"


The abrupt call halted Light, who half-turned, inclining his head with a mildly questioning look.

With his head twisted back and peering up at the other boy, L spoke, "Other than the newly received tapes, there is something else I would like Yagami-kun to see."

Light turned fully. "Yes?"

Instead of replying, L dropped his feet to the floor and reluctantly pushed himself away from the armchair. He shuffled to the television cabinet, crouched down beside it and then busied himself with tugging out several tangled wires extending from a black box that laid, previously concealed, behind the white doors of the cabinet.

Light watched L with half-concealed curiosity as he approached the cabinet. Mere minutes ago, Ryuzaki had appeared depressed over the entire situation. Yet now, he seemed almost fired up about something - a little quirk tugging at his lips on otherwise deadpan features.

"What's that?" Light asked as he stopped behind L. It would have been strange for him not to question.

Ryuk's interest too appeared piqued, peering at the curious box and its numerous dials over L's squatting form.

L lifted his head from the task at hand, wires pinched between thumbs and index fingers. He eyed Light for a moment, as if assessing whether to answer the other's question. Then, he said slowly, "This is a polygraph, commonly also known as a lie detector. I believe one might come in handy if we bring in any Kira suspects."

Light's eyes flicked from the detective to the black box.

Interesting. What are you up to this time, Ryuzaki? Choosing a time when we are the only ones in this room, even deliberately sending Matsuda out, to show me a polygraph. Am I the Kira suspect you speak of?

"Shall we test it, Yagami-kun?" L asked, eyes remaining riveted on Light, watching closely for his reaction.

Light turned back to L, a smile easily touching his lips. He wasn't one to back down from an implied challenge.

"Sure," he said. "Let's test it together."

The casual tone and relaxed, almost childlike smile, made Light look completely innocent. But appearances can be deceiving - L had learnt that a long time ago.

L nodded. "Please pull up a chair and come over here."

A few minutes later found Yagami Light sitting in a chair on L's left, L himself having returned to his armchair and upon sitting, immediately drawn his legs up, bare feet pressing into the edge of soft cushion, knees close to his body. The empty coffee cup and almost empty box of donuts had been pushed to the side of the coffee table to make space for the polygraph. Wires hung between the device and grips strapped to their right arms as well as fingerplates attached on two fingers.

"So how will this work?" Light asked, staring at the blinking lights and the fluctuating lines on the polygraph's display curiously. Though he had read about polygraphs, it was the first time he was seeing one personally.

"Simply put," L answered as his fingers flew lightly over a few keys and dials. "The person or persons connected to this lie detector is asked questions. If any of his answers is a lie, the detector will sense it and the corresponding red dial will light up." L finished fiddling with the detector and looked up at Light, continuing before the other could respond, "We might as well try and you can see for yourself. For example, I may ask Yagami-kun, how many people are there in your family?"

"Four, including myself," Light answered, seeing no harm in accepting the other's 'suggestion'.

"What is your father's name?"

"Yagami Soichirou."

"How old are you?"


"Now, try lying. Does Yagami-kun have any siblings?"

"No. I'm an only child," Light replied after a brief pause, obeying L's instructions.

A blue light beside his red dial flashed for a second before the red lit up.

A small smile appeared on L's features - a redirected victory punch for Light being susceptible to the detector. "There you go."

Light nodded. "Actually, I do have a sibling who's younger than me." The crimson glow faded.

"Ah yes. I believe your father has mentioned that you have a younger sister," L remarked. Having once observed their lives from numerous angles over five days, L couldn't say that he was not familiar with the members of the Yagami household - without lying that is.

"Yes, that's right."

"Let's move on to a more important question," L leant forward slightly. He was hoping to clarify a few matters, preferably before the rest of the Kira investigation team returned - not that he minded them finding out the way in which he chose to act on his suspicions, but he would rather avoid having worried eyes pinned on him as would be guaranteed if Yagami-senior were present at such a time. "Yagami-kun, do you have a girlfriend?"

"Really, Ryuzaki. Only you would ask for gossip with such a straight face," Light remarked in a joking manner; a fleeting flicker of red light and his free hand reaching to smooth out the bottom of his already straightened shirt were the only signs of his possible abashment.

L waited.

"Yes," Light finally said.

"From the university?"


"From outside the university?"


"More than two?"


L peered at Light the way a predator eyed its prey.

"Why the sudden increase in girlfriends?"

He only knew that it was highly probable that the second Kira had already made contact with the first. And while Light had always been very popular amongst the opposite gender, it wasn't like him to go out with a few girls at once. L wanted not only to verify Mogi's report that morning - not that L didn't trust Mogi, but he did trust his own observation skills even more - but also to hear Yagami Light's own explanation.

"Ryuzaki!" Light protested.

"I'm curious to know," L responded plainly, looking Light steadily in the eye.

"..." Light averted L's eyes, directing his gaze to the table.

"...It was hard to refuse what they had to offer."

The red dial did not light up.

The sentence had been soft, but was clear in the quiet room. It seemed unmistakeable what it implied.

There was a long pause. Then L spoke. "Don't worry, I won't tell your father."

Light looked up at L and said sincerely, "Thank you."

There was a small pause.

The gears in Light's head turned swiftly. If the purpose of this exercise was what he thought it was - and even if it wasn't, it would be better for him to begin with such an assumption - then L could only have one ultimate question - was he Kira. Eventually, he would ask him - in a question phrased with no ambiguities, demanding a direct answer. It was what Light would have done as well.

"Well," a smile slid into place on Light's face. "It's my turn to ask, isn't it?" The tone was light, held a touch of playfulness and clean anticipation.

"I don't have a girlfriend," L stated immediately.

Light laughed. "I wasn't going to ask you about that."

"You weren't?" L asked blankly, looking as though he couldn't figure out why one wouldn't want to find out more about girlfriends given the opportunity to question another under a lie detector.

Light disregarded L's question as one of those times when the other was just acting stupid, and began seriously, "Ryuzaki, there is one thing I've always wondered.


"What is your real name?"

Silence slammed down on them, as though the surrounding air had frozen over, frosted with lightly shivering tension.

L blinked slowly.

Once, twice.

But as he opened his mouth to respond, Light spoke, smiling affably. "I'm just kidding."

The red light remained unlit.

Truthfully, Light was not expecting to actually receive an answer to his last question. This exchange seemed to have little benefit for him - since the other could openly refuse to answer any question that he thought might give his name away (and L had an atrociously high guard) - but every benefit for L - for he didn't have the privilege of doing the same without appearing suspicious.

However, every additional question he permitted L to ask in between increased the risk of giving the detective an actual clue to Kira's true identity. Hence, for now, Light could only buy time by asking questions himself - and in doing so, reduce the number of questions L would ask - while he thought of how to evade, or face, the 'final question'.

L stared at Light, his gaze dolefully reproachful. "You know it scares me, Yagami-kun. If I reveal my real name anywhere at any time, you may not see me alive the day after."

Light's smile vanished instantly. "it wasn't my intention to scare you, Ryuzaki. L, Ryuuga, Ryuzaki - they make no difference to me." All his aliases were equally meaningless to him.

L seemed to cheer up slightly.

"I wonder about Yagami-kun's name too."

"What about?"

Polygraphs drew their conclusions based on one's physiological responses, that much Light knew. There were ways to lie and possibly not be detected by a polygraph. For example, if one anticipated a particular question, one could prepare for the answer such that the probability of a significant increase in pulse rate or emission of perspiration was reduced.

Reduced, but not entirely eliminated - furthermore, Light had no doubt that a lie detector procured by Ryuzaki, with his apparently bottomless bank account, was anything less than the best - and for Light, there was no room for error.

"Why does Yagami-kun's first name read as 'light' instead of 'tsuki'?"

Light shrugged. "I don't know. Maybe my father was trying to be funky..."

Both tried to picture Yagami-senior attempting 'funky'... and exchanged an amused glance.

Or maybe he knew I'll be the beacon of light leading this world out of darkness...

"Why did Ryuzaki choose Ryuuga Hideki as your alias?"

"I was told I looked rather like him."


"You don't agree, Yagami-kun?"

"If I said I did, I would be lying." Light didn't seem to be trying too hard to hide his grin.

L appeared miffed.

Light changed the name topic. "Ryuzaki, how old are you anyway? Have you attended university elsewhere previously?"

I have to think up an infallible plan to beat the detector, to win Ryuzaki... I'm definitely able to do it!

L appeared to consider for a moment, rubbing his thumb on his lips. Then he replied, "I can't answer your question about university, but..." he looked back at Light, expression deadpan, "I'm older than you."

The red dial didn't light up.

But... what's with that smugness in the tone! As if being older meant anything. How childish.

Despite such thoughts, Light bristled.

"Yagami-kun, do you believe that death gods exist?"

Light pondered for a moment. "I used to be disbelieving towards the existence of supernatural beings. But with the recent events, I'm no longer as sceptical."

"I see. I feel the same way."

"Ryuzaki, have you liked solving mysteries since you were young?"

"Only interesting ones. I enjoy putting my mind to the challenge."

"That's why you became L?"

There was a pregnant pause, before L responded lucidly, "Yes."

The red dial remained unlit. Even though their association in the past two months had given Light enough grounds to believe that Ryuzaki possessed the mind of a genius that one would expect from L, it was good to confirm it.

"But," L added in a casual tone. "I'm not the only one playing the role of L."

It was true - Watari played the part sometimes.

Light's watching eyes narrowed imperceptibly as he noted the absence of red light out of the corner of his eye.

"So you've mentioned before."

He was doing it again. Bringing these other L's into the picture.

"You seem very interested in me as L, Yagami-kun. Do you want to be L?

Light blinked at L's sudden question.

"Well," Light's eyes softened as he turned them from L and upon the opposite sofa thoughtfully. "Since I was young, I've wanted to follow in my father's footsteps and become a law enforcer, bringing criminals to justice."

His gaze flicked back to L who was watching him intently. "I guess L's accessibility to having all the world's police at his command is something I envy."

The red dial didn't once light up.


Of course, why hadn't he thought of that before?

It was obvious. The foolproof way to avoid the detection of a lie was... not to lie at all.

"I see. You desire a high level of control?" L observed, calmly sieving out the first moving line of a boy's honest dream.

There was a tensed pause.

And then, Light let out a bark of laughter devoid of merriment. L was undeniably surprised.

"You still don't trust me, do you, Ryuzaki." Light's voice was tinged with some bitterness as he accused. "All this talk about treating me as a friend earlier in the afternoon. You still suspect me of being Kira and your purpose of showing me this lie detector is merely to question me under a circumstance where I would be forced not to tell untruths. Isn't it?"

"Yes, you're right. My suspicion of you as Kira still exists; I never did say that it had ever gone away."

L didn't care to deny Light's accusations. He hadn't made any effort to hide his intentions to begin with and had rather thought that Light, with his intelligence, would realise them rather quickly. However, what he hadn't quite expected was the other openly confronting him about it, on the supposition that Light was Kira of course; the action actually pointed to Light not being Kira. Hm.

"But it's because I treat Yagami-kun as a friend that I wish to clear up the situation."

Light continued to glare at L, remaining silent and looking decidedly unappeased.

"If you're not Kira, you wouldn't mind me asking one question to satisfy my curiosity, would you? After which, we can have some donuts for tea." L gestured generously to the white donut box on the table.

"Even if I minded, it wouldn't stop you from asking, would it?"


"Then, just go ahead," Light said dryly, folding his arms across his chest and pointedly looking away from L. "But I'll decline the donuts. I'm supposed to buy some groceries for my mum on my way home and I'll probably have to get going soon or I may not be able to get them." Then he added, casting a sideward glance at L, "Didn't you just have donuts anyway?"

"That was dessert for lunch."

"...I see. Well," Light looked away again, "You only need to ask one question to get what you want."

His eyes then shut, chin raised ever slightly in proud defiance.

L stared unblinkingly at Light, bringing a thumb to his mouth. His mind spun rapidly as he chewed lightly on the end of his thumb. Though his visage remained deadpan, a fire was coursing through his blood. His nerves were tingling with excitement. Had they finally reached the end? Could it be that simple? - the dubious thought crossed his mind. He was anticipating either a confession or a lie from Light - and if it was the latter, the highly-sensitive lie detector would surely pick it up, L had absolute faith in Watari's judgement of quality.

Yet, he felt a premonition that somehow it wasn't going to work. Just a feeling gnawing at the edge of his mind. Something about Light's responses thus far. He hadn't quite liked them. No, such submissive responses just wasn't like Light.

But the only course ahead was to try.

Light's eyes were closed, but L didn't think that the boy was as naiive as to think that the detector would fail to detect his lie simply because of this, even if one's eyes were the windows to one's soul and often used to distinguish a truth from a lie by the naked eye. Furthermore, Light didn't have the opportunity to prepare any external source of stimulation that would prevent his body from responding naturally.

L opened his mouth, his lifted thumb a short distance away from his lips.

"Yagami-kun, you just have to answer yes or no," L said slowly, his voice crystal clear in the quiet room.

"Are. you. Kira?"

A heavy, expectant pause.

The sounds of breathing and the soft whirring of the polygraph became incredibly pronounced.

Eyelids slowly lifted.

The red light flickered briefly.

Light turned his head, meeting L's piercing gaze.

In that instant when their eyes locked, something akin to confusion flashed in Light's eyes. Yet, it vanished so quickly that even L wondered if he had really seen it.

Light blinked slowly.

Then, his lips parted, enunciating a single word.


L snapped his eyes away from Light, staring down at the red dial on the lie detector.

One second.

Two seconds.

Three seconds.

The red dial remained unlit.

L found himself biting down hard on the thumb that had subconsciously returned to being between his teeth. He was hardly aware of any pain the act caused, mind sent whirring at the lack of response from the polygraph.

Could he be wrong? Could it be possible that Light truly wasn't Kira?

L looked up, once again staring into Light's eyes.

Of course, he hadn't been certain that Light was Kira. But he was the most likely suspect. And it all matched. Light's intelligence and character. L's own analysis of Kira's method of thinking and personality. They had matched. The intelligence, the pride, the childishness, the competitiveness, the innocence. Could all that have been wrong? Was it all... him being blinded by his obsession to prove that Light was Kira? Blinded to the suspicion of other suspects? Merely him wanting to fit the nearly-perfect all-rounded university undergraduate to the nearly-perfect murderer?

No... it must have been something else. A strong gut feeling told L that his suspicion of Light was correct. He favoured concrete evidence, but his instinct - influenced by his subconscious brain - often proved to be as accurate. Light must have found some way to beat the detector. He must have been ly--

"I said no. My answer isn't a lie," Light repeated calmly, as if reading L's mind.

The red dial remained stubbornly unlit.

It was as if a huge weight had slammed into L, knocking all the wind out. Nevertheless, L maintained composure as he spoke clearly.

"I give up on finding Kira."

The red glow appeared instantly.


Any harder and he would draw blood. Light observed the thumb in L's mouth, feeling the urge to grin in triumph. However, he did know that doing so at this point in time would hardly be appropriate or wise. Thus, instead, he asked, "Ryuzaki, can't you believe me?"

A picture of innocence. From the wide eyes and creased eyebrows to the sincerity in the tone.

L pulled his thumb out of his mouth and clenched his teeth tight.

After a few moments, he unclenched his jaw, and calmly began dismantling the wires connecting them to the detector.

Light stood, waiting as L walked up to him and removed the wires from his person.

L spoke as he stepped away from Light, numerous wires between his fingers and thumbs. His tone did not betray a note of tension. "I'm glad to have your personal assurance that you are not Kira, Yagami-kun. Thank you."

"Anytime," Light responded steadily. "I'm glad we did this if it allowed you to lift your suspicion of me being Kira off me."

Both were well aware of the lack of sincerity in their exchange. But there was no red dial to light up now.

"Well, I'll take my leave for today," Light said, glancing at his watch.

L nodded somewhat distractedly, motioning for Light to show himself out.

"Watari," L said quietly after the door to the hotel suite was closed.

"Yes," Watari's voice sounded from the speakers, confirming his presence on the other end of the connection and that he had been listening in on the prior exchange.

"Get Matsuda-san and Aizawa-san, when he leaves the police testing department, to conduct a thorough check on all of Yagami Light's girlfriends who we know of to date. I want the results as soon as possible."

The messy bangs that hung across L's eyes hid his expression.


L leaned back into the luxurious softness of the sofa, raising his eyes to the ceiling. Desire for the pleasures of sex or a boost to their ego through feminine worship was not abnormal for males after reaching puberty. It was hardly considered uncommon for eighteen-year-olds. But to have so many girlfriends clinging onto him for that purpose was too troublesome - L recalled the vague response "it was hard to refuse what they had to offer" and mused - it wasn't like Yagami Light.

"Apples..." Ryuk prompted as he watched Light put yet another orange into his basket.

Light remained silent but his hand moved over to the mountain of apples, and Ryuk smiled his eerie smile.

Sometimes, ignorance wasn't quite bliss - what one didn't know could hurt one. As he walked along the street, Light was laughing inside despite his unaffected exterior.

"Can I eat one now?"

Light promptly ignored Ryuk.

It was fortunate that Ryuk, despite his refusal to take sides, had his one weakness for apples.

"Can I eat-" Ryuk broke off mid-question to begin a low cackle.

Light would have turned to send a glare at the Death god and see exactly what he was laughing at if he wasn't being followed. As it was, he didn't have much time to ponder about the cause of Ryuk's peculiar behaviour, for the answer soon revealed itself in the form of an all-too-familiar, annoying female voice.


Misa and Rem provided sufficient entertainment that Ryuk, wisely, only brought up the topic of apples after their departure.

"Tomorrow is L's... no, at least, Ryuzaki's, Ryuuga's death day."

"Oh, you've decided?"

The corners of Light's lips rose slightly.

"Can I have my apple now then?

Rising from his chair instead of responding, Light wordlessly walked to where he had left his bag and opened it.

The hand he slipped in emerged with an apple.

Ryuk's beam stretched from ear to ear with approval.

"Then, just go ahead." Light said, turning his face away from L and meeting the eyes of Ryuk who was still standing by the television cabinet.

"But I'll decline the donuts. I'm supposed to buy some groceries for my mum on my way home and I'll probably have to get going soon or I may not be able to get them."

Light held Ryuk's gaze.

"Oi, that's unfair." Ryuk protested.

Light looked away for a moment to glance at L, as was natural for the content of his sentence.

You had time to consider. Light turned back to Ryuk.

"You only need to ask one question to get what you want."

Do what you will.

He closed his eyes, knowing that Ryuk would succumb to his craving for apples. He had been moaning about not being able to eat them through the day since Light informed him in the morning that there were none left at home.

He was not disappointed.

He heard Ryuzaki begin, "Yagami-kun". And then, Ryuk's voice, pressed close to his ear, drowned out the rest of the question.

The feeling of the Death god's mouth against his ear was unnerving. There were no breaths, yet it sent shivers down his spine nevertheless.

Not that Light had minded that particularly. What had caught him off guard was the question; it made him want to glare at Ryuk in resentment.

"So, Light. He just told you that you are his first friend. Do you treat him as a friend? Would you rather have him as one rather than as an enemy?"

Light let his teeth clench, slight enough for the action to go undetected, before releasing the pressure. Ensuring that L was no longer speaking, he opened his eyes.

Did he treat Ryuzaki as a friend? Brilliant as Light was, it was extremely rare for him to find someone whose mental capabilities he truly acknowledged in the people around him; and amidst the desire to have Ryuzaki dead was an undeniable admiration and respect for his abilities, a recognition of an equal. Would he rather Ryuzaki have been his friend?

Light met L's bottomless pitch-black eyes.

He could hear Ryuk cackling softly beside him.

He was enjoying this.

Damn Death God.

Tossing the apple to Ryuk, Light fell back onto his bed, letting his back sink into the mattress as he stared at the ceiling.

He had decided - he wouldn't want to have met Ryuzaki any other way. Being on opposite sides of the chess board was what allowed him to truly appreciate Ryuzaki's intelligence. Furthermore, it was only when the opponent was such a worthy one that victory would be the sweetest.

Very slowly, a smirk formed on Light's lips.

Yes, victory. He would have preferred to find out Ryuzaki's real name and kill him personally. But no matter, today was already a battle won; and soon, he would also win the war. Once Rem did what she was supposed to do, he would win the war.

Ryuk stood upside down against the wall, savouring his apple, looking upon Light with much amusement. The boy was motionless but for the trembles that ran through his body - evidence of the laughter that escaped his lips.


"Let me try. Ryuzaki, how much sugar do you think you consume on average a day?" Light looked expectantly at L who had looked down and was staring at his hands.

After a long time, L finally looked up at Light and said, "I don't know."

The red light lit up.

Date started: 26 June 2005
Date completed: 30 March 2007

Feedback and concrit are welcome and appreciated.

I've drawn some sketches of some of the scenes in this fic. They can be found in the Gallery section of my website, Hidden Dreams. (Link in profile.)

For anyone recovering from The Event in anime episode 25 (manga chapter 58), I had previously written a few fics spurred by it after reading chapter 58. They are 'L' and The Right Combination. Both fics, as well as the earlier-mentioned Toothache, can be found under my ffnet profile.