1943’s Earth’s Last Citadel is a standalone far-future adventure by C. L. Moore and Henry Kuttner.
Alan Drake’s desperate bid to get genius Sir Colin out of a North African war-zone is stymied when the two are ambushed by Axis agents Karen Martin and Mike Smith. Karen and Mike catch up to Alan and Sir Colin just after the pair stumble across a mysterious object in the desert. The Nazis barely have time to gloat before they and their prey are bewitched into entering what appears to be an alien spacecraft.
The four do not emerge from their captor’s craft for a very very very long time.