Linda (Stella Stevens) and Jeff (John Saxon) are having an affair. Linda is married to Paul, and Jeff to Anne. Linda hatches a plan, where she shoots Anne and they frame Paul for the murder. They have done such a good job of planting evidence and arranging things, that no one, not even his own lawyer, believes Paul.
When Paul finally gets his lawyer to believe him, the lawyer devises a crazy scheme. They hire a voice actress to imitate Linda, and record her talking about the murder. Jeff is brought in alone for questioning. They play the tape, and Jeff falls for it, thinking Linda is trying to pin things on him. Jeff talks and reveals everything.
The movie ends with Linda in jail.
Thanks Joseph C!