The Fall of Chronopolis — Barrington J. Bayley

The mighty ships of the Third Time Fleet relentlessly patrolled the Chronotic Empire's thousand-year frontier, blotting out an error of history here or there before swooping back to challenge other time-travelling civilisations far into the future.

Captain Mond Aton had been proud to serve in such a fleet. But now, falsely convicted of cowardice and dereliction of duty, he had been given the cruellest of sentences: to be sent unprotected into time as a lone messenger between the cruising timeships. After such an inconceivable experience in the endless voids there was only one option left to him.

To be allowed to die.