"Dagger of the Mind" is the ninth episode of the first season of the American science fiction television series Star Trek. Written by Shimon Wincelberg (under the pen name "S. Bar-David") and directed by Vincent McEveety, it first aired on November 3, 1966. In the episode, the Enterprise visits a rehabilitation facility for the criminally insane where the chief doctor has been using a device which destroys the human mind. This episode introduces the Vulcan mind meld. The title is taken from a soliloquy by the title character in William Shakespeare's play Macbeth. Plot The USS Enterprise, commanded by Captain Kirk, makes a supply run to planet Tantalus V, a colony where the criminally insane are confined for treatment. The facility's director is Dr. Tristan Adams, a psychiatrist famous for advocating more humane treatment of such patients. After the Enterprise delivers supplies and receives cargo from Tantalus, a man emerges from the container taken aboard and assaults a technician. Reaching the bridge, the intruder demands asylum, but Spock subdues him with a Vulcan nerve pinch. In sickbay, the intruder identifies himself as Simon van Gelder, and a computer check reveals that he is not a patient, but Dr. Adams' assistant. When they inform Tantalus of van Gelder's capture, Dr. Adams claims that van Gelder's testing of an experimental treatment device on himself is responsible for his disturbed condition. McCoy, suspicious, urges Kirk to investigate. Kirk transports down to the colony with one of the ship's psychiatrists, Dr. Helen Noel. Adams introduces them to a strangely emotionless therapist, Lethe, and gives Kirk and Noel a tour of the colony. Although he is affable and accommodating, his staff, like Lethe, all seem lacking in affect. Adams shows Kirk and Noel the treatment device he referred to: a "neural neutralizer". He claims that the machine, harmless at low intensity, is used only to calm agitated inmates. Noel is satisfied with his explanation, but Kirk remains suspicious. On the Enterprise van Gelder becomes increasingly frantic, warning that the landing party is in danger, but when he tries to explain the danger and refers to the neural neutralizer, he is convulsed with pain. Spock mind-melds with van Gelder to enable him to tell his story. Spock learns that the neural neutralizer can empty a mind of thoughts, leaving only an unbearable feeling of loneliness, and that Adams has been using it on inmates and staff