Trapper is shipped home while Hawkeye is on R&R. Hawkeye speeds to Kimpo with Radar to catch Trapper's plane, but they just miss him. While they are there, they pick up BJ Hunnicut and take him back to camp. On the way back, BJ is introduced to the Korean War.

Scotland, the near future. Something is smashing oil rigs off the Scottish coast, and UNIT have been called in to investigate. The Doctor discovers a colony of shapeshifting Zygons and their cyborg weapon, the Skarasen, and in the process solves one of Scotland's greatest mysteries...