"Dagger of the Mind" is a first season episode of Star Trek: The Original Series. It is episode #11, first broadcast November 3 1966. it is written by Shimon S. Bar-David Wincelberg and directed by Vincent McEveety .

Quick Overview: The Enterprise visits a prison planet where a new treatment for the criminally insane has deadly results.

On stardate 2715.1, the starship USS Enterprise, under the command of Captain James T. Kirk, makes a supply run to the Tantalus Penal Colony. Transporter technician Berkeley tries to beam cargo down, but is prevented from doing so because a security force field is activated. The colony drops the field and beams a container of research materials to the ship, however, the box contains Dr. Simon van Gelder, former assistant to the prison warden Dr. Tristan Adams.

Appearing very stressed, Gelder subdues Mr. Berkeley and makes his way to the bridge, with a phaser in hand. Once there, he demands asylum, but is subdued by Mr. Spock. Dr. McCoy feels something is wrong and wants to keep Gelder on board for examination. In the meantime, Captain Kirk and Dr. Helen Noel, the ship's psychiatrist, and an acquaintance of Kirk's who he met at a Christmas Party, beam down to the colony to investigate what is going on.

Gelder tries to inform Spock and McCoy about a brainwashing device called a neural neutralizer that the warden has been using to control not only the inmates, but the facility staff as well. He warns that Kirk and Dr. Noel are in grave danger. Spock then mind melds with him to get a clearer picture of the incredible story. Once Spock learns Gelder is telling the truth, he assembles a landing party, but discovers the prison's security field is back in place, and prevents any further transport or communication to the planet. All he can do now is wait.

Down on the planet, Kirk and Dr. Noel meet Dr. Adams, and get to observe the neutralizer being applied to a patient. Adams claims the machine is perfectly harmless and is only used to stabilize and calm deranged inmates, but Kirk is suspicious. Kirk wishes to examine the neutralizer, and agrees to use it on himself, only if Dr. Noel has control, and it is used at the minimum intensity. The test begins, and Dr. Noel suggests that Kirk take his mind back to their Christmas party encounter. Adams then wrenches controls of the device, and turns the neutralizer to high intensity, forcing Kirk to drop his phaser and communicator. As a result of the neural scrambling, the delusional Kirk falls madly in love with Dr. Noel and wishes only to be with her forever at the colony. The two are then easily taken prisoner.

Later, Dr. Noel manages to get away through a ventilation duct, but her escape is reported by Lethay, a "cured patient". Kirk is saved from having his mind seriously harmed during a second neutralizer session when Noel shuts down all power in the prison complex, which in turn disables the security field. A guard corners Dr. Noel in the field control room, but she manages to push her attacker into a high voltage transformer. With the lights out, Kirk regains his wits and then subdues Adams and his assistant in the diversion. Spock, noticing that the field is disabled, beams down the security force and restores power to the colony.

During the treatment room scuffle, Kirk manages to push Adams into the reactivated machine where he is subjected to his own neutralizer, then dies as a result when it completely empties his mind. Gelder recovers and is put back in charge of the colony, and he promises to destroy the neural machine.

External Links