In this classic science-fiction story, a professional adventurer name Frank Pembroke is aboard a cruise ship that encounters a mysterious green fog and then explodes! The last thing he remembers is rowing away from the ship, but he wakes up in a strange hotel in a city he has never heard of. And, even stranger, the city is completely isolated and seems to have no way out of it.
Frank meets an extremely friendly young lady who describes herself as "the paramour type", and soons realizes that though the natives may seem normal, there is something very odd about them. He soon realizes, too, that his life and the lives of many others are in peril if he does not find a way to escape from the city and warn others of it's sinister purpose.