Randall & Hopkirk (Deceased) (2000 series)

Randall & Hopkirk (Deceased) was a 2000-2002 British television series about a private investigator (Bob Mortimer) who teams up with the ghost of his murdered ex-partner (Vic Reeves) to solve crimes. The series was a remake of the 1969-1971 British television series of the same name.

Mental Apparition Disorder (Season 1, Episode 2)
Marty's ex-fiance Jennie (Emilia Fox) overhears Jeff talking to Marty. Since only Jeff can see Marty, Jennie is convinced that Jeff is having a mental breakdown and has him sent to a sanitarium run by the villainous Dr. Lawyer (Hugh Laurie). Unbeknownst to Jeff and Jennie, Dr. Lawyer is using hypnosis to make his patients commit crimes for him. Instead of treating his patient Lucy (Fiona Allen) for sex addiction, he hypnotizes her into seducing wealthy men and stealing from them.

Dr. Lawyer plans to turn Jeff into another one of his minions, and when Marty interferes, he erases Marty from Jeff's memory and continues to brainwash Jeff. When Jennie tries to rescue Jeff from the sanitarium, Dr. Lawyer orders Jeff to kill her. Luckily, Marty has been learning how to operate in the afterlife and has discovered how to impersonate the living. He uses this power to impersonate Dr. Lawyer and stops Jeff from killing Jennie. When Dr. Lawyer orders the other patients to kill the three, Marty and Jeff manage to turn them against Dr. Lawyer instead.

Whatever Possessed You? (Season 2, Episode 1)
Jeff and Jennie check into a charming old hotel in the countryside, only to find that it is haunted by the ghosts of an evil couple who died in a tragic fire 50 years before. Jennie is possessed by the woman's ghost.