The Variable Man

The Variable Man is a short story by Philip K. Dick that can be found in his collection of short stories named "Beyond Lies The Wub".

Warning: Wikipedia contains spoilers.

In the story, the Terran system (our system) is growing all the time, but an old and corrupt Centaurian Empire is holding Terra down because it encircles the Terran system and wont let the humans grow out of their current empire. For this reason Terra is at war with Proxima Centauri and is trying to find a way of breaking out from the Centaurian noose around its neck.

In the war, Terra is continually coming up with new weapons to try and break Centaurian defenses, but Proxima Centauri is also continually updating its defenses. Using spies and other such tactics both parties find out about each others advances, and no actual fighting ever happens because both sides are too busy trying to beat each other with technological developments. Eventually Terra comes up with a concept for a bomb, that Proxima can not defend against. Then the odds start to side with Terra, and Terra prepares to fight with it. The only problem is that the bomb does not yet work.

This is where the Variable Man comes in. The Variable Man is a man from the past. He is brought into the current (or future depending on perspective) via a Time Bubble as an accident. He escapes from the authority in the future and spends a lot of time running from them afterwards. It is, however, discovered that this man has a certain genius to fix things and make things work. This is because he comes out of a period when humans had this natural genius and knack to invent things and solve problems. It is at this point that the man working on the FTL (Faster than Light) bomb realizes that The Variable Man is the only person who can make his bomb work. And thus, he gets him to help out.

The bomb eventually works, though not in the way that anyone would have guessed. I will leave to rest to you to find out...

Go read the story.