In the opening scenes of the episode, the evil double (whose name is never revealed) enters the restroom and encounters the real Barbara. She asked Barbara for her lipstick because it was the only thing she could not match, right before she shot and killed Barbara with a silencer. The mistress than puts on Barbara's lipstick and meets Stefan, while posing as Barbara.
Monk, who is on a plane with Sharona on their way to meet her aunt, notices something amiss when he sees Stefan and Barbara. The first time they were shown, the real Barbara had to stand on her toes to kiss Stefan. The double does not. It is later revealed that the real Barbara Chabrol (née Lesser) is a trust fund baby; her family owns Lesser Pharmaceuticals. The mistress killing Barbara was part of Stefan's plan to continue living off Barbara's riches, by passing her off as Barbara. She would later trap Monk in the lavatory while Stefan poisoned Bernard, an old friend of Barbara's. After Barbara's body is found by Randy Disher, who Monk called about the case, the evil mistress was arrested along with Stefan.
- Barbara Chabrol's double is the first of two female evil twin/clones to appear on Monk; Patrice Gesner is the other.