The Armageddon Machine — Simon Kewin

The last, battered remnant of the feared Draconian starfleet limps through space, shadowed by ships of the victorious Million Star worlds. But the Draconian ship is still a terrible threat: it is the Draconian's final weapon, a device that can trigger the cascading collapse of space/time itself.

Mackenzie, in charge of the Million Star fleet, fears what will happen if he attempts to destroy the device. Then, one of the semi-mythical Xin ancients arrives on his ship, suggesting a plan that appears to endanger all of reality. In the final battle with the Draconians, Mackenzie must decide whether to trust the Xin or not. The fate of the universe itself hangs on his actions...

A science fiction novella in the Golden Age tradition.