Fredric Brown reprises the popular image of Martians as little green men, who are around 75 cm tall and have small torsos, long frayed limbs, and spherical bald heads.

Unlike most other fictional Martian invaders, the Martians that Brown writes of do not intend to invade Earth by violence but instead spend their wakeful hours calling everyone 'Mack' or 'Toots' (or some regional variation thereof), reveal embarrassing secrets, heckling theatre productions, lampoon political speeches, and even provide cynical colour commentary to honeymooners' frustrated attempts at consummating their marriage.

The nonstop acerbic criticism stops most human activity and renders many people insane, including Luke, whose stress-induced inability to see the little green maligners divides opinion on whether he should be considered mad or blessed.

Galaxy reviewer Floyd C. Gale praised the novel, saying that although Brown was occasionally "carried away," he nevertheless "succeeded in writing a very funny book.

"[3] The novel is considered a classic of science fiction by the following works of reference:[4] In 1990, director David Odell adapted the novel into a movie of the same name with Randy Quaid playing the title character renamed to Mark Deveraux.