Cliff Ross, Jr. awakens in big trouble. A girl is dead, there's evidence he was in some kind of fight and he can't remember what actually happened. Unless Mannix can help him reconstruct events, he's likely to go to prison.

Mannix is brought to a small town in New Mexico under false pretenses, where he is then served a subpoena and must testify as an expert witness for the prosecution in a murder trial; he stays on the trial as the aid to the defense.