This is a short science fiction story (like The Outer Limits). It's about a convict (ex military) who has the choice between death or being injected with some alien virus.
He is slowly transformed into an alien. When the transformation is complete, the humans want to kill him. He escapes, while they (humans) send a unit after him. He doesn't kill any of them. In the end, they catch him, but before they can kill him the aliens come to his rescue.
One of the humans or aliens said,
They are not ready yet!