13 Darkest Star Trek: The Original Series Moments

After an accident with the transporter during an ion storm, Kirk, McCoy, Scotty, and Uhura are horrified to find themselves in a distorted version of their own reality, one where cruelty is expected and murder is an acceptable way of advancing in the ranks. To blend in, they must adopt the same depraved attitudes of those around them, no matter how much it sickens them.

Adding to the stress of the unfamiliar surroundings, it's literally a race against time to get back to their proper universe. If they miss the narrow time frame that's available, they will be trapped in this nightmarish parody of their home for the rest of their lives.