Second Contact, by Mike Resnick, paperback science fiction novel
“It looked like a no-brainer to defence attorney Major Maxwell Becker. A starship captain has gone a little crazy and killed two of his crewmen in cold blood. Just plead insanity, make sure they give his client a nice, comfortable, padded cell, and go skiing at Aspen.
But the captain refuses to cop an insanity plea. He insists that the two crew members he killed were not humans, but aliens. That’s his story, and he’s sticking by it. So Becker reluctantly goes through the motions of trying to prove his case–
–and suddenly his witnesses start getting transferred or disappearing, and when he finally finds one he realizes there are holes in his story… and suddenly Becker is running for his life, hunted by every branch of the military. He can’t figure it out: he’s a loyal officer, he’s just doing his job as a military attorney, he’s never broken a law, there are no aliens: so why does everybody want him dead?
Join Hugo- and Nebula-winning author Mike Resnick as he chronicles Becker’s desperate attempt to learn the only thing that can save him: the truth.”