One night, Bobby Zierath hears strange noises in his closet. He opens it to discover that the TARDIS has materialised inside. He joins the Doctor, Steven and Vicki for a series of adventures. They visit a planet with giant talking mushrooms (called "mooshroos" by Vicki) and ancient Rome, fight robots that looked like drills, rescue Vicki from the "Most High" and meet Conidrons and the Zaksi. Bobby is returned to his home moments after he left (by repeatedly pressing the fast return switch) and leaves the TARDIS with HiFi, given to him by Steven.