The Mentalist Episode 5.02 Devil's Cherry

While the team investigates the murder of a diamond cutter who was eviscerated with his own tools, Jane is more distant than usual due to the disappearance of Lorelei Martins, his link to Red John. After drinking a cup of tea from the victim's house, Jane uncovers a rabbit that was locked in a cabinet and chases the animal into a neighbor's yard. There, he meets a precocious young girl who claims to be his daughter - the same one who was killed by Red John along with his wife. As Jane reels, the team uncovers his barely conscious body on the floor of the house. The tea he drank contained belladonna, a poisonous hallucinogen, and the existence of the girl was entirely in his mind. As Jane recovers and attempts to work the case, he has to cope with the fact that the hallucination of his daughter has decided to stick around for a while in order to help him solve the crime.