The menace of Chatalia.
Chatalia… a fantastic artificial world, inhabited by furry winged creatures with awesome powers. Here Kirk, Spock and their Enterprise mates, trapped, face terrifying death. And if by some miracle they escape, they will confront the roving killers of the dread Klingon Empire!
The Enterprise encounters a generation ship during a routine survey mission. Nothing beamed in can be beamed out again, and the ship draws energy from anything near it, while the race of humanoids within debates what to do with their captives.