Mind Light (original 1992; edition 1992)

Amazon.com Product Description (ISBN 0345377184, Mass Market Paperback)

Disheveled, disoriented, and ill, Greg Lukas didn't look like much of a pilot. But the Michaelsons, a family of interstellar traders, had to hire another crew member or lose the ship that was their livelihood. So they took Lukas on temporarily, assuming that he was a good pilot with a bad attitude.
But Lukas's problem was much deeper: as a pilot in the Space Corps, he had stumbled upon a secret a powerful Corps faction would do anything to hide. His mind had been invaded and his memories rewritten, but the process had damaged him, perhaps beyond repair. Now he was tortured to the edge of endurance by the return of memories meant to be blocked forever. Lukas was falling apart -- and his rediscovered knowledge had put him in danger once again. When the Michaelsons learned who Lukas really was, they were willing to protect him -- but they were no match for his enemies. Unless help came from a surprising direction . . .