The Depths of Time — Roger MacBride Allen

Time is of the essence when you're stranded in the future....

Humanity is running out of time.

The settled universe is filled with terraformed worlds linked by timeshafts -- temporal wormholes in deep space. These timeshafts are the only way to travel the vast distances between the stars.

The Chronologic Patrol is charged with guarding the timeshaft wormholes and preventing time paradoxes at all costs. But one critical mission ends in disaster, turning Anton Koffield, captain of the Upholder, into a dark legend....

As ships carrying relief supplies to a crippled planet approach a timeshaft, they are mercilessly set upon by mysterious attackers -- their crews are murdered and the sanctity of time itself is at risk.

In response, Koffield is forced to do the unthinkable: he must stop the invasion by destroying the timeshaft. Marooned eighty years in the future, he lives as a cursed figure, the villain who killed a world.

And his odyssey through time has only just begun....