"Dagger of the Mind" sticks Kirk literally into a torture chamber, not quite the idyllic "resort" expected on a visit to the Tantalus Penal Colony. As Enterprise delivers infra-sensory drugs they inadvertently take aboard an escapee from the Colony, a Dr. Simon Van Gelder, usurped director of Tantalus. Van Gelder's colleague, the slick-talking Dr. Tristan Adams, is full of suspicious stories that pique McCoy to press for an investigation (and thereby save Van Gelder from Kirk's merciful return). Accompanying the captain (at McCoy's delicious selection) is Dr. Helen Noel, technical expert on psychology and veteran from what must have been a smoldering Christmas party.

Spock and McCoy interrogate Van Gelder above while the investigation under the impenetrable Colony forcefield continues below. Kirk insists Adams explain the Neural Neutralizer that ostensibly damaged Gelder, but the explanation doesn't quite fit. Spock employs the Vulcan Mind Meld (for the first time) to unlock the truth. Adams uses the device to painfully brainwash his victims and provides Kirk with exceptionally close personal experience. "And now, she's gone," as Kirk musters enough deteriorating will ordering Noel into the airducts to interrupt the forcefield's power. (Fortunately penal colonies have ducting large enough for surreptitious crawling.) At Helen's success Kirk escapes forcibly while Spock beams in, unknowingly restoring full power to the Neutralizer with Adams caught beneath it.

This suspenseful story is fueled by strong supporting performances from the guest stars, like beautiful Marianna Hill as Dr. Helen Noel. Renowned character actor James Gregory does an effectively sinister job as Dr. Tristan Adams, flawlessly pouring three perfect shots (in how many takes one wonders?). Morgan Woodward appears here in the first of his two unforgettable TOS roles as the tormented Van Gelder, to whom remembering even his name brings pain, terrible pain. (Woodward wields a wicked karate chop in any incarnation!) Suitably menacing in the background are also "I love my work" Lethe and the eerie Eli. The Neural Neutralizer chair deserves a guest appearance itself, an immediately recognizable Trek symbol.

The Tantalus colony offers a glimpse at Federation Penal systems that will be complemented by "Whom Gods Destroy" later in the series. Helen saves Kirk with her sufficient knowledge of hypervoltage and strength to wrestle a duct cover open (could Kirk's inability be an artificial inhibition about escaping in any way?). Kirk has his "smug button-pushing brasshead" attitude extinguished in a powerful lesson that mirrors the poetically appropriate demise of Dr. Adams, left to die alone in the treatment room without even a tormentor for comfort.