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.

• David Kane

• Bill Paterson
• Lucy Griffiths
• Peter Guinness