A/N: This came about after I wondered what would've happened if the Doctor and Martha had arrived in Cariff just a little bit earlier...
The scene takes place during Torchwood, the end of season 1, episode The End of Days. They have just completed the retina scans and are about to open the Rift.
The four Torchwood dissenters stood around the Rift Manipulator. Jack's recently shot body lying lifeless on the floor next to them. Gwen typed in the emergency override procedure. A warning sign popped up. She hesitated for a moment, turning around to look at her team members. They couldn't make eye contact with her, couldn't let themselves succumb to doubt. This was the time to back out. But she couldn't; she needed Rhys back. She was about to hit the 'OK' button, but all of a sudden, there was a whooshing noise. The four living Torchwood members turned their attention to a blue police box that appeared out of nowhere in the middle of the Hub. A young woman opened the door and stepped out.
"This doesn't look like Cardiff," she said to someone who must have been behind her. "I think you got the coordinates wrong." She suddenly saw the quartet staring at her. "Oh-"
A tall, skinny man stepped out of the blue box and stood right next to her. "Well, maybe the coordinates are off a smidge, but we're definitely in Cardiff. The TARDIS readings tell me this might have to do with some recent activity coming from the Rift; its energy pushed the TARDIS away so that it couldn't land in the designated area." He realized the woman wasn't listening, and soon noticed what she'd been staring at. "Oh, hello. Sorry to interrupt whatever it is you're doing. We'll be off."
"Who are you people?" asked Gwen, taking a slight step forward. "How'd you get in here?"
"Oh my God, this man's been shot!" said the woman, running to kneel over the limp body lying on the floor. The man walked to her side, not taking his eyes off the body.
"Always getting into trouble," said the man, hovering over Captain Jack's corpse. "Never listens to me... That's not true, actually; I'm probably one of the few people he does listen to."
"What?" asked the woman, turning up to face him. "Do you know him?"
"Used to travel with me," said the man. "But that was some time ago." He suddenly cocked his head to observe his surroundings, noticing the logos on the walls. "Wait a minute! Is this Torchwood? Oh no... No wonder you killed him. It's because he knew me, right?"
"I'm sorry, but who are you?" asked Owen, a bit confused, a bit annoyed, and a bit frantic.
"I'm the Doctor... Do you not know who I am?"
"Um... no," said Owen.
"Well, that's a bit humbling," said the Doctor. "But I mean, this is Torchwood! The only reason it was formed was because I got Queen Victoria mad at me."
"You met Queen Victoria?" asked his companion.
"Yeah, back with Rose," the Doctor sighed. "This was a while after I last saw Jack, which was in the year 200100, as I recall."
"Is that where he's from, then?" asked the woman.
"No, Martha," said the Doctor. "He's from the 51st century, but I actually met him in 1941."
"Boy, he really gets around," said Martha.
"You don't know the half of it," said the Doctor, smirking. Martha lifted an eyebrow. Tosh, unable to contain herself, burst out laughing.
"Oh, so you do know him then?" said the Doctor, turning to the group of four.
"He's our boss," explained Tosh. "Was."
"Wait!" said the Doctor, wide eyed. "He works for Torchwood?!"
Jack, always with the perfect timing, gasped back to life. The first thing he was able to process as his eyes came back into focus was a very angry looking man staring at him and shouting, "You work for Torchwood? How could you?"
Jack rose to his feet and asked, "I'm sorry, have we met?" He then noticed the police box. He stared at it, then looked back at the strange man, then back at the police box, then at the man again. "Doctor? Is that you?"
"Of course it is," he said. "Why are you acting like- oh, right! New face. How'd you figure this was me?" Jack pointed at the TARDIS. "Oh, right," said the Doctor.
"Doctor," started Martha. "How did he-"
"But the point still stands!" said the Doctor, too upset with Jack to even pay attention to Martha. "Torchwood?"
"You don't understand," said Jack, lifting himself up to his feet. "It's different now. After what happened at Canary Wharf, I rebuilt it... in your honor."
"Oh, don't talk to me about Canary Wharf. If it happened once, it can happen again. If there's anything I've learned, it's that history has a tendency to repeat itself."
"I can handle the responsibility," said Jack.
"Can you?" said the Doctor. "You never wanted to before."
"You used to expect so much from me," Jack said. "Why can't you trust me now?"
"Because you think you're infallible," said the Doctor. "You take the risks- you thrive on them. You have to remember that there are other people who depend on you."
"Like Rose?" sneered Jack.
"What?" asked the Doctor, taken aback.
"After Canary Wharf, I saw the List of the Dead- it said Rose Tyler."
"Oh, no. She's alive."
"What?" asked Jack, his turn to be surprised.
"Yeah," said the Doctor. "Sorry. Living in a parallel world, safe and sound. And Mickey. And her mother."
"Oh, yes!" said Jack, a wide smile on his face. No matter what his feelings towards the Doctor were like moments ago, his joy in finding Rose to still be alive warranted a hug.
"Who's Rose?" asked Gwen, mystified by the strange circumstances under which Jack was having a strange conversation with a strange man.
"Oh," said Jack. "How do you describe Rose? She was amazing, beautiful, funny, caring..."
"Brilliant," added the Doctor.
"Fantastic," continued Jack.
"Good old Rose," mumbled Martha, rolling her eyes.
"Oh, sorry," said the Doctor, remembering his manners. "Jack, this is Dr. Martha Jones. Martha, this is Captain Jack Harkness."
"Pleased to meet you, Martha Jones," smiled Jack.
"Stop it..." warned the Doctor.
"I was only saying hello," said Jack, defensively. He suddenly turned to Ianto and said, "Really, just hello." Ianto nodded, a slight blush forming on his cheeks.
"Okay," interrupted Owen. "That's all very nice, with the your little reunion and all, but I'm still opening the Rift now."
"What?" gasped the Doctor. "Why?"
"They think their lives will be magically better if they do," said Jack. "I tried to stop them, and, well, you saw what happened."
"Trust me," said the Doctor, turning to Owen. "Whatever you think is going to happen, it isn't going to turn out that way. The Rift is dangerous. You can tear this universe apart."
"That's a risk I'm willing to take," said Owen, quickly pressing the button to open the Rift.
The ground instantly began to shake, and alarms blared in their ears. "What have you done?" asked the Doctor.
They quickly escaped from the collapsing Hub. Gwen and Ianto helped move a still weak Jack. When they reached the safety of the streets, Gwen said, "It's all right, Jack. Everything is going to go back to normal." But then she saw him: Bilis Manger standing solitary ahead of them.
The Doctor watched and observed silently as Bilis said, "From out of the darkness, he is come."
"What is he talking about?" asked Gwen.
"The song of the Great Beast cast out before time, chained in rock, and imprisoned beneath the Rift," said Bilis.
"What?" asked Gwen again.
"All hail Abadon, the Great Devourer, come to feast on life."
The group turned, awestruck by the sight before them. A great monster appeared in the distance, destroying everything in its path.
"The whole world shall lie beneath his shadow... I look upon my god and know my work is done."
"Doctor, what do we do?" asked Martha, panicked.
"I've got an idea," he said. "Jack, follow me."
"Exactly what I was thinking..." said Jack, obeying his command. They found the closest open space- a nearby empty field.
"What?" asked Gwen. "What are you going to do?"
"This thing feeds on life," Jack explained. "Well then, wait till he gets a load of me. I'm an all you can eat buffet." He turned back to the Doctor. "How long have you known?"
"Ever since I ran away from you," he said.
Jack nodded. He gave the Doctor a solute and turned toward the open field.
"Jack!" cried Gwen, starting to run after him.
"Let him go," said the Doctor, grabbing hold of her her arm to stop her. "He knows what he's doing."
"Bring it on!" cried Jack. He steadied his pose. Abaddon spotted him and started to come over. Jack's screams could be heard across the field as Abaddon feasted on his life force. But, finally, they fell silent as the great monster dropped to the ground, defeated by the man who couldn't die.
It had already been a few hours since they carried Jack's body back to the Hub.
"He's really dead," said Tosh.
"But he can't die," said Gwen. "He told me so."
"But that's impossible," said Martha. "Everyone dies. Right, Doctor?"
"It's true," said the Doctor. "He can't. It's a very long story that happened a very long time from now. But this Abaddon creature soaked up a lot of his life force, so the healing process is taking a lot longer than usual." He paused for a moment to think. Then, a flash of genius. He started rummaging through his pockets."But maybe I can help with that."
"You?" asked Owen. "How can you help?"
"With this," he said, pulling out a small device. "Sonic screwdriver."
"Sonic what?" said Owen.
The Doctor aimed his screwdriver at Jack. After only a few moments, the color returned to his face. His eyes shot open as he sat up gasping for air.
Gwen rushed to hug Jack. Next came Tosh, followed by Ianto. Owen walked over, his head bowed down in shame. "I'm sorry," he whispered.
"It's okay," said Jack, pulling Owen into his arms. "I forgive you." Owen wept silently and then slowly backed away.
Jack finally turned to the Doctor. "Who looks at a screwdriver and thinks, 'Ooh, this could be a little more sonic'?"
"What?" said the Doctor. "You've never been bored? Never had a long night? Never had a lot of cabinets to put up?" Jack and the Doctor both smirked, until, suddenly, Jack stopped.
"You abandoned me," he said angrily.
"You don't need me," said the Doctor.
"That may be," said Jack. "But you left me on an lifeless space station, surrounded by Dalek remains. I had just revived from being exterminated, and had no clue why. I heard the TARDIS dematerializing in the distance. And now I can't die... ever. So maybe I don't need you watching out for me, but I certainly needed answers, and I needed you as a friend. I've been waiting a very long time to find you again, so what I want to know is: what happened?"
The Doctor sighed. Jack was right; he deserved to know. "Rose."
"But I thought you sent her home?" asked Jack.
"She came back," he said. "She absorbed the Heart of the TARDIS, which no one was ever meant to do. She couldn't control it. She brought you back, but she brought you back forever."
"Can she fix it?"
"I took it out of her," said the Doctor. "I'm sorry."
"Jack," Gwen stepped in. "What's going on? These friends of yours appeared out of nowhere in a big blue box, you died, he revived you by pointing some gizmo at you, and you're keeping the rest of us in the dark. So would you please bring us all up to speed because it's really infuriating when you do this."
Jack stared at her for a moment. "Fair enough," he said.
"Tell me," said the Doctor to Gwen. "Can I ask you, is your family from this area?"
"Generations," she answered, taken aback by the question. "Why?"
"No reason," he said, smiling broadly. He knew she looked familiar...
"You're just as strange as Jack," she said. "You two related?"
The Doctor turned to Jack, and said, "Are you my Mummy?"
"Oh God!" laughed Jack. "That still freaks me out! I can never look at a gas mask without cringing now."
"And he's still doing it," said Gwen, wondering why she even bothers.
"I know how you feel," said Martha, walking over to Gwen. "This one never tells me anything, either."
"So," said Gwen. "How'd you end up traveling with him?"
"He invited me," said Martha. "How'd you end up working for Jack?"
"He hired me," said Gwen.
"Well," I suppose this is goodbye, then," said Jack.
"I suppose," said the Doctor. He paused for a moment before adding, "You could... come with me."
All eyes were on Jack as they waited for his response. "Thanks," he said. "But no. I kinda like it here. Got a good team."
The Doctor nodded his approval, and he turned to leave. "Wait," said Jack suddenly.
The Doctor turned back to face him. "Yes?"
"I was wondering... could you fix this?" he said, holding out his wrist to display his Vortex Manipulator.
The Doctor chuckled. "No way," he said, causing the captain to frown. "You could go anywhere. Twice. Second time to apologize."
"Can't blame a guy for trying," he sighed. He turned to Martha, taking her hand and bringing it to his lips. Martha blushed. The Doctor rolled his eyes. "It was nice to meet you, Martha Jones."
"You too, Jack," she said, smiling.
Ianto stepped forward, a little too quickly. "Are you sure there's nothing else we can do for you before you leave?" Which secretly meant, leave right now before I decide to handcuff Jack to the chair in his office. Hmm... not a bad idea.
"No," said the Doctor. "It was nice to meet you all."
There was one final round of goodbyes as the Doctor and Martha stepped back into the TARDIS.
"Well," sighed the Doctor, fiddling with the controls. "That was an interesting day."