'Dagger of the Mind' by S. Bar-David (a.k.a. Shimon Wincelberg)

Doctor Simon van Gelder, a member of the psychiatric staff at the Tantalus Penal Colony, comes aboard the Enterprise seeking help. Realising that van Gelder is exhibiting signs of manic insanity, Doctor McCoy insists that Captain Kirk investigate the prison. Despite the facility's exemplary reputation, Kirk agrees to follow up the Doctor's suspicions, and he takes the ship's psychiatrist, Doctor Helen Noel, down to the facility. Here they learn that the director of the colony, Doctor Tristan Adams, has been using a brainwashing device called the Neural Neutralizer to control not only the inmates, but also his staff. In an attempt to prove that the machine is perfectly safe, Adams convinces Kirk to try the machine for himself. However, the director then uses the device to alter the captain's mind, making him fall madly in love with Helen Noel. Adams then takes the two of them prisoner. Meanwhile, van Gelder is too distraught to explain to Lieutenant Commander Spock what is going on at the penal colony - forcing the Vulcan to attempt a mind-meld with the unstable man in an attempt to discover the secret of Adams' unethical activities...

William Shatner (Captain James Tiberius Kirk), Leonard Nimoy (First Officer Lieutenant Commander Spock), DeForest Kelley (Doctor Leonard H. ‘Bones’ McCoy), Nichelle Nichols (Lieutenant Nyota Uhura), Larry Anthony (Ensign Berkeley), James Gregory (Doctor Tristan Adams), Morgan Woodward (Doctor Simon van Gelder), Marianna Hill (Doctor Helen Noel), Suzanne Wilson (Lethe)

Directed by Vincent McEveety

TX:
3rd November, 1966

Notes:
*Featuring Captain James Tiberius Kirk, First Officer Lieutenant Commander Spock, Doctor Leonard H. ‘Bones’ McCoy and Lieutenant Nyota Uhura