"It was all a lie." Stiles' broken sob reached Derek in the hallway. Derek was leaning against the wall near the stairs, his arms folded, looking up at the ceiling. Derek had been compelled earlier to shake Stiles to get more information about what was going on. But he wasn't prepared for Stiles to cry. Derek even covered his ears as Peter started soothing Stiles with the voice of a practiced father.

Was Stiles really this torn up over this? Over him? He wasn't even sure what was going on. Peter also seemed bewildered to what was happening. Apparently a double of Derek had snuck in and slept with Stiles while Derek was absent. Derek closed his eyes, grimacing as Stiles made a choking noise that crawled under his skin and into his chest. Hearing it was bad enough, but sensing the fear and sadness in waves like being drowned in heartache. God, what had this imposter said in his image to get Stiles so attached to him? And apparently had sex with with Stiles in his image. That wasn't RIGHT. Derek gritted his teeth, wanting to tear this fake into pieces. Stiles had to be one of the most annoying persistent people he knew, but he was useful and clever; and he didn't deserve to sound so ruined.

The silence fell like a thick wall of smoke and Derek moved silently into the room. Peter was sitting quietly, looking down at the boy that was half in his lap. Stiles' arms were tucked into his chest, his hoodie hood pulled over his head and there were damp spots. It looked as though he'd been trying to hide as he cried. He was sound asleep now. Peter lifted his head as he slowly rubbed Stiles' shoulder and held up a finger to his lips, signaling silence. Derek drew closer, sitting on the stool Peter had earlier abandoned. He leaned his arms on his knee, leaning closer to Stiles, in his stupid red hoodie. His face looked blotchy and pale and the dark circles under his eyes were hard not to notice. Derek decided to rip his own face from whatever had impersonated him before he mauled it to death.

"Derek," Peter's breath was soft, speaking bellow whispering, "He should sleep with the pack for a bit. They'll help him heal." Peter was staring at him meaningfully and Derek gave a slight nod.

Peter gently gathered the boy in his arms; lethal killing weapons that would have dispatched Stiles months ago. Peter was as silent and steady as carrying a child upstairs and returned within the minute.

"What's going on?" Derek asked as soon as Peter reached the bottom step.

"I have a theory." Peter swiftly went to his laptop and started it up.

"And that is?" Derek followed Peter as his uncle sat in half a chair and Peter paused, glancing at Derek.

"Worried about Stiles?" Peter quirked an eyebrow.

"NO." Derek's teeth snapped sharply and then he drew in a deep breath, "I'm worried about this thing walking around with my face. Now what's the theory?" Peter tapped his fingers on the wood desk top, eyes rolling upward in thought.

"I think... it has been doing this for long term benefits." Peter closed his eyes to piece together all the little bits of information, "Stiles was completely convinced it was you. It even smelled like you. I'm guessing it also acted like you if it was around for 3 weeks."

"What is it after?" Derek asked and Peter pondered until his eyes opened quickly, sitting up more in his seat.

"I think it was getting exactly what it's after." Peter said and started clinking away on his mouse pad, "I remember a story my grandfather," He pointed at Derek, "Your great grand pappy," Back to the laptop, "told us on a hunting trip." Peter spoke in a slightly older, and somehow more cryptic tone as he impersonated 'great grand pappy', "There is a creature from which even your dreams are not safe, my boy. Creatures that roam the night and your greatest pleasure will be your own demise." He added a cryptic low key chuckle and glanced at Derek, who was very still. Derek would not admit that it was somehow more terrifying than when Peter was an alpha. Peter cleared his throat, looking back to his laptop, "Grand pappy also thought computers were a fad and that they would go back to carving things in stone. But in the ways of legend, he WAS our source of information. Much like the Argents have their book." the PDF popped up and Peter smiled wryly, "Twisted old dog had quite the devil's streak." He got a look from Derek that told him to hurry up. Peter rolled his eyes and scrolled through the pages, "You have to learn to listen to your elders some day."

"What is it?" Derek stressed and Peter paused on a page that had a picture of a luxurious bed with someone sleeping in it. And there was a transparent gargoyle like thing resting on the human's gut. It was ugly and probably accurate.

"It sounds like an incubus. Or at least, part of an incubus." Peter lightly pointed on the screen to the archaic Latin, "They are spirits that come into ones sleep and have sex in one's dream. They gain energy from it, like you or I eat food."

"You're saying Stiles dreamed it all?" Derek asked and Peter shook his head slowly.

"No, Stiles is too intelligent to mistake it for a dream. He was truly convinced it was you. Flesh and blood you. And plus, an incubus may go unknown for years. It doesn't take that much energy. It's only a spirit. I showed you the incubus because I think what we're dealing with is spawned from an incubus." Peter started typing on his computer with the swiftness of someone half his age and Derek watched over his shoulder, frowning at the information that was loading in on crappy wifi. Derek grimaced at the terrible old drawing that Peter popped up. It reminded of the terrible weasel and wolf pictures that were supposedly werewolves.

"A Cambion." Peter presented with a hand under the picture. Derek studied the image. It was of a naked looking renaissance woman with small boobs and luscious hips, only covered by a sheer strip of cloth, touching some young man's face with small fingers and she held in her hand a plant with roots attached. Peter began to summarize the old text, "Legends tell of a mortal creature born of a human woman and a demon called an incubus. An incubus lays with women, drawing up the image of the person that woman loves and seduces her in her dreams. And if done enough and with some preparation on the incubus' part, they will conceive a child."

"Fascinating." Derek glared at Peter, not wanting a history lesson of where the thing came from. Peter rolled his eyes.

"The cambion is thus, a shape shifter." Peter scrolled down the page, "It can take form of the person it collects essence from. Once they take that person's essence, they have that person's memories, thoughts, and body; and since it has taken from you, and you are a downright prude, I think it was from that snake that bit you last month."

"I'm not a prude." Derek huffed.

"Of course not." Peter said with the slightest bite of patronization, but he did not mock his nephew for long, "Cambion, which is singular and plural, mind you, will then seduce the person who is most attracted to the body they are taking. They can almost sniff it out. Now, here's why." He tapped on the screen which Derek couldn't read anyway because it was in Latin, "The cambion feeds on sexual energy, just like its sire did. It is said that it can eat human foods as well, but they thirst for the energy of their victim. Side effects may include; a weakened state of health, increased mental stress levels, fatigue, physical aches and pains. Sound familiar?" Derek remembered Stiles' weakened body and nodded, "Cambion use this plant, ginseng to help reduce the symptoms and will allow their food source to live longer. And I did smell the hint of the herb on Stiles' breath. Like their sire, they like long term relationships and teenagers are a prime source for a full course buffet."

Peter took a deep breath and continued, "Because taking sexual energy, or any energy that will take away from the victim's bodily functions, they try to keep their victims happy and healthy. And since the cambion takes the form of someone the victim finds attractive, it's very likely that the victim will fall in love with the cambion version of the person. No matter how much of a prick the real person may be." Peter's eyes flickered to Derek for a split second and Derek was more than annoyed with the side banter, "It says that in plain Latin. Not me, I swear." Peter clears his throat, "At the cambion's disposal is of course, shape shifting, taking the memories and desires of its victims, high intellect in most cases, and also a natural drug they produce to help their victims into the mood."

"Drug?" Derek asked, "Like the plant?"

"No, no, it's sort of..." Peter waved his hand abstractly, "Sort of how a poison dart frog is poisonous by eating poisonous insects. Sex is the cambion's food source and its weapon. If their victim isn't in the mood one prick can turn that mood 180."

"So a starved cambion is a weak cambion." Derek concluded, rubbing his chin between his fingers.

"Yes... but good luck finding a starved cambion." Peter said, "It's been feeding from Stiles for 3 weeks, so I'm sure it's built up quite an artillery." Peter gave a wry grimace, appearing concerned, "Stiles concerns me."

"If the cambion is gone, it'll help him get better, won't it?" Derek looked to his uncle and Peter looked up at Derek.

"Not because of the cambion stealing his energy." Peter said and Derek's gaze traveled to the stairs. He almost heard the echo of broken sobs in his ears again and he quickly refocused on the computer screen, "Stiles came here, hoping to court you."

"Then he's more of an idiot than you take him for." Derek spoke through gritted teeth, "The cambion probably did it to him." Peter twiddled his thumbs, looking like he wanted to protest outright but he simmered his words.

"Cambion seek out the person most attracted to the form they take," Peter turned back to the passages, "There is no power in seducing someone who does not have passion for the form they take. Impassioned people have the more vibrant energy." Peter smiled at the screen, tilting the screen back a bit so he could see his nephew when the screen went dark. Derek was listening, "Love can cure a kamina. Love can feed a cambion." Derek snapped the laptop screen shut, leaving some scratches on the top of the plastic.

"He's 16. He's not in love." Derek said drew away from the table, going back to his duffel, knowing they needed washing from the long trip, "How do we kill it."

"The cambion or my brick of a laptop?" Peter asked with raised brow, "Because I think my laptop has just experienced severe trauma." Derek ignored the quip and Peter opened the laptop again to check. Derek glanced towards the staircase and tried to ignore the urge to go check on Stiles... and his pack. His pack of course was more on his mind. Not Stiles, "It doesn't say."

"What do you mean, it doesn't say?" Derek frowned, "There's not another cryptic riddle for you to solve?"

"Well when a cambion is discovered, it usually moves on to the next victim." Peter tapped his chin with his finger, "It's odd, it talks a lot about how intelligent and how well it adapts to its environment. The acting can be flawless because it takes from the memory of its form. Hm..."

"I'll just have to find it, and rip its face off." Derek, eyes wandering back to the stairs again, forgetting about washing his things for now, though he started to pace, becoming anxious.

"It's not suggested," Peter told him, his eyes starting to follow Derek, "Cambion don't just look like you and act like you. It is strong like you, has your memories and is intelligent." Derek made a frustrated noise, still looking at the stairs, "And you shouldn't see him until he's more stable." Derek looked to Peter, realizing what he was doing.

"I wasn't thinking of checking on him." Derek then started looking everywhere but the stairs. Peter stood, closing his laptop gently, remembering that Derek had not been this antsy, even when they got back with injured pack members.

"I meant when he wakes up." Peter told him. Derek stopped, frowning at his uncle.

"Why?" he turned to face Peter.

Peter gave him a well knowing look, "Because obviously he's just had his reality turned upside down and his heart has been stomped on. I don't think he's ready to be sorting out his feeling for the real you right now. It'll only confuse him." It was logical and sound, but Derek hated that it made sense.

"I didn't DO anything." Derek stated, standing straighter.

"Please Derek, this is very delicate and let's face it," Peter pinched his fingers together, as though showing a fine line, "you are not good with delicate things. Running your angry mouth will only hurt him further." Derek visibly gritted his teeth and ground them, "He's hurt and there's nothing you can do to help in this situation."

"Don't remind me," Derek snapped and by passed his uncle to go into the kitchen. He hated to feel useless.