Micromegas is a six-hundred-and-fifty-year-old, thirty-nine-kilometre-high giant from the planet Sirius who can speak a thousand languages and has been expelled from his homeland for writing a heretical tract. On Saturn he befriends the local secretary of the Academy of Sciences - a comparative dwarf, being only two kilometres high - and the two decide to travel to earth together, where they will make startling discoveries about human nature.