Set in the 23rd century, the series followed the further adventures of the crew of the Federation starship Enterprise, continuing on from the original Star Trek series. In this episode, the crew of the Enterprise re-visit a "shore leave" planet for R&R but quickly find themselves under attack.
On stardate 5591.2, the Federation starship Enterprise crew revisits a fondly remembered "amusement park" planet, hoping for some rest and relaxation.
The crew discover the planet's Keeper, who had overseen the operations of the facility, is now dead and the untended machinery is constructing dangerous images from the crew members' thoughts. Lt. Uhura (voiced by Nichelle Nichols) is captured by the planet's master computer (voiced by James Doohan), who in the wake of the Keeper's death, resents being made to serve others and also seeks to "liberate" the Enterprise from what it perceives as slavery. To this end, it takes control of the Enterprise computer and starts manipulating the ship's systems.
After a number of unpleasant adventures and narrow escapes, Captain Kirk (voiced by William Shatner) succeeds in interviewing the angry computer. He convinces it that its best course is to resume business as usual, as it will be rewarded with social contact by the many guests attracted by the planet's facilities and can, in time, learn everything it could possibly want to without even being put to the inconvenience of leaving its home planet.