A/N: This is set directly after episode 5 of Children of Earth and contains spoilers of that series. It is however AU, for reasons that will be obvious.
Disclaimer: Don't own Dr Who or Torchwood.
Jack hit the ground with a thump and groaned. Then he froze in shock. Instead of the smooth tiled floor he had expected in the bay of the ship he was trying to board he found himself face down on a metal grill, the kind of which he had only ever seen in one place before. He slowly rolled over and stared. Sure enough, the coral supports of the TARDIS were clearly visible next to him, and he could hear the rhythmic whirring of the time rotor in the background, the constant sound that indicated they weren't moving.
He sat up and looked around. A figure appeared from around the other side of the consol wearing a distinctive pinstriped suit that Jack instantly recognised. Struggling to his feet he approached the Doctor.
"You bastard," he spat as they got closer. "You had to come back, now when it's too bloody late, didn't you."
The Doctor shook his head. "If it had been up to me I'd have left you to it," he replied. "Everyone deserves a chance to grieve for what they have lost."
Jack stared. "Then why are you here?" he asked, confused.
The Doctor glanced at the doorway that led into the rest of the TARDIS. "Like I said, it wasn't my decision."
Jack growled slightly, getting annoyed. "Stop playing word games Doctor. If it wasn't your decision, then whose was it?"
"Mine," a voice spoke up from the doorway. Jack froze.
"Don't you think it's a bit dangerous, crossing timelines like this?" He asked softly. "I mean, he didn't know me until he joined Torchwood 3, so isn't it a bit foolish to introduce us before then?"
The Doctor sighed. "Jack, he already knows you."
"Oh, he kept that one secret then, I mean, you'd think I'd've noticed that a member of my team went travelling with you. Still dangerous though. And cruel."
The Doctor grimaced. "It would be cruel if what you hypothesised was true. But it's not. He knows you from later than that."
"No…" Jack breathed softly. "No. He died. He died in my arms because of my stupidity."
"I did die," the voice agreed. "But you of all people should know that death isn't always permanent."
Slowly, so so slowly, Jack turned around. There, stood in the doorway, was his one time colleague and the one man he had truly loved, apart from the Doctor.
"Ianto…" he whispered, as if even saying the name might make him disappear.
The figure smiled. "It really is me," Ianto added softly when it became clear that the Captain wasn't going to move. He stepped forward from the doorway, which was all the cue Jack needed, and within seconds he was holding the now sobbing older man, gently rocking him and murmuring soothing sounds in his ear.
"You were dead," Jack choked out, clinging to the younger man with all his strength. "I watched you die, and it was all my fault!"
"Shhhhhh," Ianto murmured, gently manoeuvring them over to a bench at one side of the room and lowering himself onto it before pulling Jack down next to him. "I'm not dead, I'm here, and I'm not going to leave you again, I promise."
Jack just clutched the front of his shirt harder, burying his face in Ianto's shoulder. He'd spent over 6 months believing his lover had died that night, and to have it revealed that he was still alive was almost too much to take in.
Finally, what seemed like much later, he lifted his head and wiped his eyes on his sleeve, not letting go of Ianto. He still wasn't entirely sure that this wasn't some really cruel dream.
"So why make me wait so long?" he asked finally, aiming his comments directly at the Doctor. "I mean, I'm guessing from how well he knows the ship that you two have been working together a while, and this is a time machine anyway, so WHY THE FUCK DID YOU LET ME THINK HE WAS DEAD FOR 6 MONTHS!" He was screaming by the end of the sentence, sobbing again despite his best efforts not to. Ianto wrapped an arm around his waist and pulled him back to lean against his chest, rubbing soothing patterns on his back.
"We did try and find you before now," he replied softly, ignoring the fact that the comment had been addressed to the doctor. "We've been trying for a while, but you were shifting around so often that it was hard to get a trace on you, and although this ship is brilliant and all she isn't the best at hitting the right date and time. Actually, that might be more the fault of the driver than the ship, but the point stands. We kept arriving too late, to be told that you'd already gone. This was the first time we could get a strong enough trace to intercept you."
The Doctor moved forward from the console. "Oi, my driving isn't that bad…well, ok, maybe it is, but that's beside the point."
Ianto shot him a glare that quite plainly said 'shut up' and turned his attention back to Jack.
"Cariad, if there had been any way of contacting you earlier I would have taken it, I promise you. I love you Jack, I wish I'd said it before, and I'm not going to leave you, I swear."
Jack nodded slightly and twisted to bury his face back in Ianto's shirt. Ianto sighed and gently pushed the other man far enough away that he could stand up, hauling Jack to his feet. "Come on, time for bed, and I'll explain things when you've had some sleep. Goodnight Doctor."
He received a small wave as he led Jack down the corridor and into a bedroom that the TARDIS had helpfully moved closer to the control room. He guided the older man through the door and led him to the bed.
"Come on, strip off some of those layers and lay down, we'll talk in the morning."
Jack slowly began to do as he was told, looking like a lost child as he peeled off his braces and unbuttoned his shirt. Ianto quickly did the same, stripping to his undershirt and boxers before climbing into bed and patting the mattress, beckoning Jack to come and lay beside him.
Similarly attired the older man settled down beside him, instinctively reaching out for contact as if to reassure himself that Ianto was still there. Ianto sighed very slightly and snuggled down beneath the covers before wrapping an arm around his lover and pulling him close.
"Get some sleep," he whispered softly, using his free hand to gently play with Jack's hair as he had done when they were together before. It took a while, but gradually his breathing evened out, although his death grip on Ianto's shirt never faltered. Ianto just lay there, playing with his hair and mourning for the happy, carefree Jack he had used to know. He would be that way again, he knew, but he hated that he should have been the cause for so much heartbreak.
Finally he settled down and closed his eyes. He didn't really need to sleep these days, but it would help pass the time until Jack was calmer and ready to talk. They always said sleep helped, and he really hoped they were right.
When Jack woke the next morning the first feeling he got was confusion. Where was he? And who was he snuggled up against?
Very faintly he could hear the sound of the time rotor, and everything came back to him in a rush. His talk with Gwen, beaming up to the cargo ship, landing in the TARDIS, the Doctor, Ianto... Oh god. He was sure he wanted to open his eyes, scared it had all been a dream and he'd wake up with some random stranger.
Ianto woke instantly as he sensed Jack's breathing pattern change from asleep to awake. He didn't move, staying in Jack's arms, and he could feel when the other man began to doubt the truth of the night before by the slight tightening of the arm that was firmly wrapped around him. The fear he could sense in his lover was enough to convince him to make a move.
"Morning," he said softly, shifting slightly to face his partner. "Sleep well?"
Jack's eyes opened slowly. He blinked, as if he wasn't sure what he was seeing was real, and then slowly his face broke into a smile.
"It was real?" he asked incredulously, shifting until he was laid on his side facing the younger man.
Ianto grinned. "It was real," he agreed softly, lacing the fingers of one hand with Jack's. Suddenly the hand he was holding tugged hard, and he found himself laying on top of the Captain and being kissed like their lives depended on it. He smiled to himself and kissed back, relishing the contact they'd been denied for so long. When they finally broke for air, not that it was really necessary but Jack didn't know that yet, Ianto just smirked and commented "I take it that you missed me then?"
The response was another kiss, and they spent a happy 10 minutes or so making out on the bed, not going any further, just delighting in being together again. Finally Jack drew away.
"Not that I'm trying to kill the mood or anything, but how are you here? I mean, you died in my arms from the poison the 456 put in the air, and you were still dead 2 days later, so how come you're alive now?"
Ianto laughed slightly. "Ah, now that's the question, isn't it. The short version is, because of you."
Jack glared. "That's not an answer. If I'd brought you back like I did when Lisa killed you you'd have been awake before I left."
Ianto shook his head. "Oh, you didn't mean to bring me back, but you are the reason for it. Let me start at the beginning, 'cos it's a bit hard to explain."
Jack nodded and settled down to listen, still keeping contact with his lover. Ianto snuggled down beside him and began. "Right, well the easiest way to explain is to go from when I woke up after I died. It was about 4 days after I died as far as I know, and from what people have told me you left the day before. Well, anyway, I woke up in the morgue, feeling rather confused as you might imagine, and suddenly there's this man in a suit stood next to me saying 'hello, I'm the Doctor'. Well, I knew who he was from Torchwood, but it was still a bit of a shock to not only be alive but to be meeting him. He took me back to the TARDIS and explained that he'd sensed something that wasn't meant to exist, that being me, and so he had come to investigate. Turns out I was registering as a fixed point in space and time, like you do, but he could tell I wasn't you for reasons I don't fully understand."
Jack interrupted. "So, what, you're saying you're immortal?"
"Shhh, let me finish," Ianto reprimanded gently. "I'm getting there."
Jack huffed and subsided.
Ianto grinned. "Right, where was I. Right, so after he'd explained this whole fixed point thing to me, with most of it going straight over my head, he took me to the lab and ran a whole load of tests on me to see if he could find out why I was suddenly like you. And he got an answer."
"It would appear you have given me STI," said Ianto lightly.
Jack sat up slightly. "That's not possible," he denied. "I was vaccinated against every possible disease when I joined the time agency, I can't catch them or carry them."
Ianto shook his head in reproof. "No, I said you gave me STI, not AN STI. This is a new disease, one that you seem to have created."
Jack sighed. "Alright, I'll bite. What exactly is STI?"
Ianto grinned. "Sexually Transmitted Immortality," he said, a hint of amusement in his voice. "You made me immortal by having sex with me."
Jack just stared. "That's not possible," he said eventually. "I mean, for a start if I made people immortal by shagging them then why did Estelle die? Or Alice's mother?"
Ianto shifted slightly. "Now that's where it gets interesting," he said. "It would appear that there are some very specific requirements to catch it from you. It works mainly on the basis of genetic transfer, such as the kind that is exchanged through kissing and sex, but it lies dormant in most cases."
"Except?" Asked Jack curiously.
"Well, it would appear that for it to take effect there must be genetic transfer after death, something to do with there being no need for immortality if you're already alive. The kiss you gave me on floor 15 happened to be just after I died, and it was enough of a genetic transfer to make the dormant disease become active. But because it was new it had to rewrite some of my DNA, which is why it took so long for me to wake up."
Jack just stared. "You mean to say that I made you immortal by shagging you."
"And this has all been confirmed by the TARDIS's equipment?"
"Yep. All checked and documented. Only problem is that we've found a couple of drawbacks to the immortality thing."
Jack looked worried. "Which are?"
Ianto touched his arm gently. "Nothing life threatening, well, not really. It's just that while it takes specific circumstances to catch it from you, with me it's not so difficult, in fact I'm highly contagious. Anyone I have sex with will become immortal, and that would be a bad thing according to the Doctor."
"Yeh, I can see that," replied Jack, his tone trying to hide his urge to burst into laughter but not really succeeding.
"Which is where you come in," commented Ianto, his tone suggesting it would be a good idea not to laugh. "If I can't have sex with a mortal, then my only other option is to have sex with an immortal. AKA, you."
Jack couldn't help himself. He laughed. "You mean the main reason you looked for me is because you're horny?" he choked out between breaths.
Ianto glared. "Hey, 6 months is a long time to go without it when you've been used to it nightly, which I was if you remember, seeing as you were the one to initiate most of it. So forgive me if I don't fancy abstaining for the rest of time."
Jack forced himself to stop laughing. "Right, well, we'll see what we can do to remedy that problem shall we?" he suggested with a leer, rolling them over until he was straddling the younger man's legs.
It was Ianto's turn to laugh. "Now there's the Captain we all know and love," he spluttered.
"And don't you forget it," replied Jack with a smile, before leaning down to press a kiss to his lovers lips. "We've got forever, and I plan to make the most of it."