Dr. Douglas Monaghan and his his two assistants investigate the case of Carol Fleming, a personal friend of Monaghan's, who sees her double, Helen Reid, at a local museum. The women chat over coffee and learn that they share the same taste in art and are both married to men named Gordon. When they realize that they are the same age and have the same birth date, they realize they must be twins. Monaghan is interested in Carol's dreams where she sees herself and twin girls watching a doll's house burning. He invites Carol and Helen to come to the lab to see if they have a telepathic connection as well and they score an almost unbelievable 100% on the test. After an auto accident in which her husband is killed, Helen moves in with Carol temporarily but but Carol begins to worry when her husband shoes an interest in her identical twin. Carol has her own secrets however and as their relationship deteriorates, so does their telepathic ability.

Helen can't understand why Carol would put her ideal home situation in jeopardy by having an affair with Mike and even impersonates her sister to break off the relationship. She's also studying the intricate details of Carol's childhood. When her boyfriend Mike is murdered, Carol has feelings of guilt and Monaghan isn't sure if she might be unstable. As Monaghan's assistants look into Helen's background and childhood, they begin to realize that she is the one who may be seriously disturbed. It becomes obvious that one is setting the other up for Mike's murder and it's left to Monaghan to sort out who is who and who has done what to whom.