The Poison Belt is a science fiction novel by British writer Arthur Conan Doyle, the second book about Professor Challenger. Written in 1913, much of it takes place in a single room in Challenger's house in Sussex.

Challenger sends telegrams asking his three companions from The Lost World— Edward Malone, Lord John Roxton, and Professor Summerlee— to join him at his home outside London, and instructs each of them to 'bring oxygen'. During their journey there, they see people's behaviour become excitable and erratic. On arrival they are ushered into a sealed room, along with Challenger and his wife. In the course of his researches into various phenomena, Challenger has predicted that the Earth is moving into a belt of poisonous ether which, based on its effect on the people of Sumatra earlier in the day, he expects to stifle humanity. Challenger seals them in the room with cylinders of oxygen, which he (correctly) believes will counter the effect of the ether.