In an African desert millions of years ago, a tribe of ape-men is driven away from their water hole by a rival tribe. They awaken to find a black monolith before them. Guided by the monolith, they learn how to use a bone as a weapon and drive their rivals away from the water hole.
Millions of years later, a scientist ventures to an outpost in space, in search of answers about a mysterious epidemic at the base. The epidemic is discovered to be a cover up; there has been an artifact discovered buried under the rock of the moon. As the scientists ride to the artifact, a monolith identical to the one encountered by the ape-men is revealed. Sunlight strikes the monolith and a loud noise is heard.
Later, a spacecraft floats through space — it’s controlled by a super computer. Aboard the ship, the passengers grow increasingly concerned about the computer’s ability to safely complete their mission, and plan to shut it down. The computer takes notice. It sabotages one of the scientists and sets him adrift in space, but after struggling for survival, the last remaining scientist tries and deactivate the computer. The robot reassures the man that it is fine, pleading with him to stop, expressing fear as it begins to die — it’s red light fading to darkness. As the man deactivates the circuits controlling the computer, it regresses to its earliest memory, a song which he sings for the man.
As the end grows near, the man notices a powerful signal aimed at the planet Jupiter. At Jupiter, the man investigates another monolith discovered in orbit around the planet. He is pulled into a vortex of flashing lights, flying through vast distances of space, seeing unbelievable things among the cosmos and the colourful lights.
Awakening in a bedroom that appears in a neoclassical style, the man sees versions of himself growing older — first middle-aged in his spacesuit, then older and dressed for dinner, and finally as an old man dying in the bed. A monolith appears at the foot of the bed, and as the man reaches for it, he is transformed into a fetus enclosed in a transparent orb of light. The new being floats in space, gazing at the Earth below it.