The Enterprise is at an unspecified starbase for a little R&R, and to pick up a few new crewmembers. The character development and backstory comes to a halt when new orders come in. The USS Bowfin, a scout ship, was sent off to do an anthropological survey, and they are well past their reporting deadline. Kirk and crew are dispatched to find out what happened.
The briefing en route fills in the details of the Bowfin’s mission. The planet they went to was pretty much uninhabited, except for a large tropical archipelago. Rather uninteresting, except for some oddities that warranted a closer look.
Looks like it’s pretty much a case of Mutiny on the Bowfin. But if that’s all there is, we wouldn’t have much of a story, would we.