The initial death is not as bad as Jack might have expected. Physically, at least. He has accepted this, after all; struggling against it wouldn't stop it. If John refused to pick up that shovel and heap dirt into the grave, Gray would activate the bomb and kill John as well, and then Gray would bury Jack without using John to do it. Either way, it ends with Jack in this grave and at least this way means one less body. And it might be even harder to bear it if Gray was the one holding that shovel instead of John.
Hard enough to know that Gray's the one who shoved him into the grave and ordered this. Hard enough to know that after all those years of searching for his brother, knowing he was to blame for whatever became of Gray, the reunion he got was a literal stab in the heart. Jack knows he deserves it. He let go of Gray's hand; the guilt is his burden, worse than the increasing weight of the dirt. But if Gray only killed Jack for it, it would be quite different from knowing that Gray killed and injured so many in Cardiff just for payback against Jack. They were innocent in this, and yet Gray set John against them because of Jack.
Gray would not have done this if Jack had not let go of his hand. Those deaths are Jack's responsibility. And now his own brother wants him to spend two thousand years dying over and over and over.
Jack hopes the team will make it through. He believes in them. If anyone can save Cardiff, it's them. He hopes Gray will be satisfied now and not hurt them any further, but Jack knows that's just a hope. They are all a part of him, and if Gray wants to hurt him, that's certainly the way to do it. Owen and Tosh and Gwen and Ianto. Ianto. This is the last thing that Ianto needs, losing Jack again. Maybe they'll see each other again after the passing of these millennia, this penance. Jack can't hope he'll have a shred of sanity left by then, though.
It would be nice if the sun was higher in the sky so he could feel a last bit of warmth before going under, but the angle is wrong and leaves the grave in shade. The dirt piles in around him and on top of him, and he can feel the cuffs biting in more from the weight of it, and the ring that John tossed onto his chest presses in as well. "Sentimental value," yeah right. Jack can't cut through his guilt and grief enough to wonder what the ring really is.
The air runs out soon enough, and though Jack holds his breath as long as he can, he can't stop his body from frantically trying to pull in oxygen and filling his lungs and nostrils with dirt. He's vaguely aware that there's still more dirt to shovel before the grave is finished, but that thought results from some hysteria as his lungs feel like bursting and he asphyxiates.
The blackness is there for him, as always. Completely devoid of senses and entirely alone. Death is no release.
He comes to life, instinctively trying to open his eyes but unable to against the dirt, gasping for air as always and only choking down more dirt, and the black swims over him again. He's aware of one distinct thought through it: Gray. Gray and blackness.
The next time, as his lungs fight hard, he realizes that the black of death has a different quality from this grave black. There is something in this black that isn't there in death's nothingness. The pressure against his eyelids and the lack of oxygen make faint colors swirl in his mind, little explosions– explosions around Cardiff to cripple the city, powerful shocks arcing through his body through the shackles. John's idea or Gray's orders? Shackles. He doesn't want that thought at all, and the deeper black pulls him under again.
Gray. Shackles. Not memories he wants. Arms spread wide, muscles strained, those first panicked thoughts when he came to life in the Hub were of metal and blood and the twisted smile of a mad Time Lord and not again. Strange how it was actually a relief to realize he was only tied up in his own base by an obsessive ex who'd shot the hell out of him. Could be worse. And yet chained in the Hub and even on the Valiant, he still had more range of movement than he has now, and he could at least breathe, except the times when the Master tried out different methods of cutting off his air. Even if Jack's ankles and wrists weren't cuffed, the loose grave dirt is only slightly dislodged by his gasps for missing air, and not at all around his fingers. He can't slowly dig out without somewhere for the dirt to go. He's smothered in the dark.
The grave is torture and Jack knows torture. His best friend's slow death. His own experiences delivering torture, interrogating– why the hell had he done that after what he'd seen? The year that never was, pain and death over and over. He both wants to know and doesn't want to know what those creatures did to Gray. Wants to understand so he can help heal his brother yet knows he isn't truly capable of it. He'd just fail Gray again. His body can't help but fail again.
Sometimes he thinks that whatever keeps reviving him has a voice. A delusion, or not a delusion, how can he tell at this point? It's something for his mind to cling to, at least. A spark of gold and his body pulling at nothing and what is and isn't Rose's voice, and the word it knows is "Life." This isn't life. This is death and death and death and Gray. The black always swallows the gold and silences it.
He is locked in his mind. His body is locked in dirt and life and death and his mind is locked in itself. He has no way out of this, no key to release him, and can only go further and further into the dark. The only thing waiting for him there is madness, not release. They can be mad together, mad brothers, one shackled to life like the other was shackled to corpses. United by death, stronger than blood. In a grave and no dust to dust because there's no end to it. Dust of Daleks. Darkness broken only by mad thoughts cresting over before drowning again.
Long ago in hundreds of years from now, he hoped and will hope that the Doctor could fix him and save him. Nothing can save him from this. No guilty conscience will drive Gray to dig Jack out of hell. In the fifty-first century, a boy will let go of his brother's hand and condemn them both. In the two thousand and second century, a formerly mortal man will wake up with dust and corpses wondering why he's alive and abandoned. In the nineteenth century, a time traveler will be trapped living through the end of a century and the start of two more, unable to travel time, unable to search for the brother he failed, unable to get answers. At the end of the universe he'll get some of them and it won't fix him. In the twenty-first century, along comes duty and love and change and it'll all be snatched away to the first century, when the brothers will reunite and he'll be dying and dying, alone in the dark.
Darkness and death and "life" and all over again. Again. And again.
Jack makes himself sick coughing up dirt, and he doesn't mind because he can cough it up and get sick now. Air finally makes it into his lungs and he would weep if he had tears for it, but his tear ducts don't seem to be working right. Maybe they're dirt-clogged, too, and he's making mud in them. It's a ridiculous thought that sends him into wild, hoarse laughter, and he's hugging the two who pulled him from the ground and voicing his amazement that it's them– he'd be amazed to see them if the sun didn't hurt his eyes.
Talking with them sobers him quickly, though. Risk of time paradoxes. Not out of this yet. He'll have to go back under and wait it out more.
Even though he's doing this willingly, it still triggers a newfound sense that he would really rather not be trapped in another enclosed space, thank you very much. He nearly panics at the thought of the black closing over him again, but they talk him through it and sedate him to keep him from being so aware of it. When he sinks back into the dark, it's with a chemical calm.
In the twenty-first century, Cardiff mourns again. A scarred city holds on together. Cryogenic machinery awakens Jack right on time to lose more of himself, and he is not frozen or locked up at all about that. He'd tried so hard to save Owen and wanted so much to see Tosh grow and grow, and instead duty caught up to them. His brother. The three left in Torchwood hold on to each other, and Gwen to Rhys and Jack to Ianto. They mourn.
Jack sits in his office behind his antique desk, staring at a slim folder waiting to hold records of his time in the dark. Just the facts. What's for sure, timeline-fixed. John and the cryofrozen Gray and Jack himself have their memories of a burial in the year 27 AD. It is the kind of history only known to those who experienced it and those they tell of it, so Jack has to record it and make it so. He writes a brief, shaky account of that and shoves it into the folder. History recorded. He sets his pen down and doesn't care where it rolls. Some older papers from the Archives go inside next: on a particular day in 1901, Alice Guppy of Torchwood Cardiff began detecting a curious repeating signal, and after three days of that, set out with Charles Gaskell to have it dug up. Also written there are the coordinates and dates, the device used to make the discovery, and other details of how it was discovered but not any hint of what was discovered. Another set of records goes in: Emily Holroyd left strict orders that nobody is to attempt to open Bay 5 in the morgue; the timer has been set to revive the subject and open the seals– a few days ago. That discovery was Jack himself of course, cryofrozen for over a century, and then woken up to face Gray again. No paper record was made of what Torchwood found in 1901 or what was in Bay 5– a Jack who was not the Jack of that time, possessing a transmitter ring which led Alice to the grave– those details were only known in the memories of a dead man and two dead women and a man who can't die, and now they are known to Gray if he was conscious to be aware of that, but these memories are still part of the timeline and the details unrecorded out of necessity to preserve reality. It worked. For over a century, Jack successfully avoided tipping himself off to his own presence there in the morgue, and thus never created a paradox by encountering himself. He can and must record those facts now to clarify what wasn't written before, and he does, as briefly as he can. The paper is shoved in with the others.
History finished for now, Jack sets an emptied tumbler on top of the folder and presses his face into his hands. That's done and it had to be done. He is deeply exhausted, but not about to open the hatch that leads down into his bedroom. No interest in crawling underground any time soon, no. The Hub is large enough that he can stand it, but the space under his office would be far too much for being far too small.
More work to do. Not the fun kind. The Rift was activated multiple times by John and Gray, and Jack anticipates plenty of residual effects from it. And because they are Torchwood, the three left of Torchwood, they will deal with it. This is what they do.
Holding the assembled folder, he realizes this is how it will happen. He leaves it open on his desk with the tumbler on top, making sure a certain concerned party will find it and wonder about it and use wonderfully clever thinking to consult another brilliant mind about what can be done. Those two will devise a plan that'll keep the timeline intact according to the recorded details while sparing Jack century after century of dying in the dark. It has already happened for Jack and Jack has ensured that it will still happen. He doesn't know when or how it will, but they're moving towards it as Jack moves away from it. If he could do something for Tosh and Owen– but that has happened and is fixed, and interfering with his personal timeline to save them would be reality-fracturing. He'd trade back being saved from the dark to save them if he could. Two more he can't save.
Life goes on. It always goes on. And sometimes a wondrous blue breaks through the darkness to offer a little light.