In 2267, when the USS Enterprise encountered a large, ringed asteroid with a class M atmosphere, Captain James T. Kirk requested that a geologist join the landing party. Freyer took soil samples, tasting one as a "good old fashioned tongue sample." Suddenly the indigenous humanoid population went insane and the landing party were forced to flee. Freyer guarded the entrance of a cavern where they'd all hidden, but soon he also went insane. He shot Leonard McCoy's medical tricorder and then, with his phaser set to disintegrate, he threatened all of their lives, calling them traitors. Spock subdued him with a Vulcan neck pinch.
In sickbay, McCoy diagnosed Freyer as having contracted Akwood's syndrome, a curable viral infection that causes temporary insanity — but the antidote wasn't working. A Giant Brain organism living at the core of the asteroid was similarly found to be afflicted with Akwood's syndrome via huge, mutated versions of the virus. Freyer had a second spell of insanity requiring a tranquilizer to calm him. This inspired Kirk to decide to try to cure the Freyer and the Giant Brain. Freyer's infection allowed him to sense the location of the viruses within the brain entity. While antibodies within the brain pursued them, Freyer led Kirk and McCoy toward a crevasse full of the viruses and leapt into it to concentrate them all into one spot. McCoy sprayed his antidote throughout the crevasse. Unfortunately it was too late for Freyer, who had been killed by the viruses. (TOS comic: "The Brain-Damaged Planet")
- While his rank was not stated in dialogue, he wore a sciences division uniform with lieutenant stripes.