Home Is the Hunter

A territorial standoff between Kirk and a Klingon commander gets interrupted by Weyland, an alien of god-like power who punishes both sides by scattering three officers through Earth's past: Sulu into a power struggle in feudal Japan, Scotty into pre-uprising 18th-century Scotland, Chekov into wartime Russia. Each has to survive on skills alone, torn between the history they've landed in and the Starfleet duty waiting for them if they ever get back.