A/N: My explanation for Spock Prime's actions in the new movie (mainly, why he wasn't able to stop Vulcan's destruction... in a roundabout way of telling it).
Spoilers/warnings: Spoilers for movie, some aspects of TOS as well as other events in the Star Trek universe
Disclaimer: Title, epigraph are Tennyson's. Star Trek is not mine. Also, my knowledge of anything outside the new movie verse is limited to watching a few episodes and researching a lot of wikipedia articles. If something is not cannon in my story, feel free to let me know.

"Old age hath yet his honor and his toil.
Death closes all; but something ere the end,
Some work of noble note, may yet be done,
Not unbecoming men that strove with Gods."
--Alfred, Lord Tennyson, "Ulysses"

Their time ended long ago.

Jim had first mentioned it to him in a conversation they'd held at the end of their five-year mission. Always an avid reader, the captain had quoted Tennyson's "Ulysses" when he declared, "How dull it is to pause, to make an end, to rust unburnished, not to shine in use!"

At the time, Spock had been baffled by Kirk's statement. They were returning from a successful mission, and they had both known then that Jim would be promoted upon their return to Earth. It was logical to assume that his career was only beginning. Therefore, Spock had been unable to determine why Jim was convinced that their greatest accomplishments had already passed.

Looking back, Spock realized Jim was far more insightful into the future than he'd ever imagined. Spock himself had gone on to captain for a brief time before becoming an ambassador--a successful career by anyone's standards.

Yet despite all of his successes, he'd never truly felt the same thrill and excitement as he had during his five years as first officer of the Enterprise, just as he'd observed that Jim was never truly in his place unless he was captain of a starship.

He'd watched as those around him advanced rank, attained success, and, in some cases, passed away. He'd mourned those deaths and moved on, burying himself in his work as ambassador in an effort to let go of the past.

On some level, he realized that his efforts to save Romulus would be his final task as ambassador. When he'd entered the black hole, he'd been partially convinced that his ship would not be able to survive the forces. Yet seconds later he'd jettisoned out of the black hole and into Nero's clutches.

He'd tried his best to escape and warn the Federation of Nero's plans. But the years had taken their toll on his body, and Nero's crew kept an exceptionally close eye on him, which meant he'd been unable to succeed in his efforts to free himself. He'd been helpless as the first seven starships had emerged from warp only to be blasted to pieces within seconds of their arrival.

But when the eighth ship had appeared, he'd felt hope. He'd seen the numbers on the ship's nacelles even before Nero had magnified the hull. It may have been an illogical response, but as soon as the Enterprise had arrived, Spock knew that somehow its crew would be able to stop Nero.

His trust in the crew's capability had wavered as he watched Vulcan implode from the surface of Delta Vega. Nero had beamed him down minutes before its destruction, leaving Spock no time to reach the outpost he knew was nearby. Seeing his planet destroyed had devastated him, and he'd retreated to a nearby ice cave to meditate and center himself.

Perhaps the crew of the Enterprise in this reality was not as capable as the crew in his own reality. If Nero had told him the correct star date, then the Enterprise would have only been launched a few years previous. That meant that its crew was more than likely inexperienced and no doubt would have been reeling from the sudden loss of seven other starships in its fleet to a ship with weapons that far outmatched their own.

Despite his age and the insurmountable odds of finding the technology to defeat Nero, Spock knew that he must find some way to finish what he started. If the Enterprise and her crew could not do it, then it logically fell to him.

He had never wished for Jim's presence more than he had at that moment. The task before him was monumental, and he needed someone to plot and strategize with, just as he had in times past, if he were ever going to discover a way to defeat Nero.

But those times had been buried with Jim on Veridian III.

His contemplations had been disturbed by the arrival of a young stranger fleeing for his life from one of the carnivorous creatures of Delta Vega. The last thing he expected to see was a much younger, very much alive James Tiberius Kirk staring back at him.

And as he built a fire in an effort to buy time to reflect on this new development, he couldn't help but smile inwardly as he thought of the final lines of the poem his captain had quoted so long ago. "Some work of noble note may yet be done," he murmured softly.

If he could persuade this younger Kirk to become captain of this reality's Enterprise, perhaps there would be hope for the universe after all.

It was time for one final mission.