A UFO lands on the moon under the cover of a meteor shower. An Alien approaches Moonbase on foot and shoots out a window, causing an explosive decompression which kills a SHADO operative. After a search, the UFO is discovered in a nearby crater, and two teams in moon mobiles go to investigate. When the UFO opens fire, the Interceptors are sent in. While Foster is on his way to get a moon mobile, he is injured and his radio disabled. The Interceptors destroy the UFO and it crashes nearby, destroying a moon mobile. Foster is presumed dead, but he is in fact still alive, as is an Alien. After initial mistrust, the two join together to try and survive the walk back to Moonbase. But will they?