While the others are preparing the Jupiter 2 for a long-awaited lift-off, Will, Dr. Smith and the Robot are collecting ore samples. Dr. Smith is injured by an explosion, and, suffering from amnesia, refuses to return to the Jupiter 2. A strange beeping noise leads Dr. Smith into a cave, and Will and the Robot follow him. They find an ancient computer and other artefacts from a forgotten civilization, but aware that the Jupiter 2 will shortly lift off, the Robot strikes Dr. Smith, restoring his memory, and the three set off for the ship.