Man's control over the machines he has created is absolute. He has manipulated his natural environment, conquered the problems of interplanetary travel, and is ready for what comes next. In the first year of the twenty-first century, 2001, you are commander of Discovery, a spacecraft traveling at a hundred thousand miles an hour. Your destination is a planet on the farthest edge of the Solar System. Your companions are a fellow navigator, three deep-freeze hibernauts, and Hal, a chatty computer who ceaselessly guides your course and your life. The mission you undertake through the abyss of space has been set off by a shrieking slab found within the Moon's crater Clavius. There is no possibility that this strange monolith is a natural formation. It is a deliberately buried calling card, left by an alien Intelligence millions of years ago. And you must find it, wherever, whatever, It is.