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.

A woman is attacked in her apartment and thrown out her balcony to her death, and the police conclude that it is a suicide thanks to a forged suicide note Mannix believe she was murdered and investigates the death.