Suburban England, 1981. 10-year-old Kevin is sent to bed by his materialistic parents when a knight on horseback bursts out of the boy's wardrobe and vanishes. The following night, the wardrobe discloses a band of vagabond dwarfs pursued by the Supreme Being, whose map of the space/time continuum the robbers have stolen. Kevin follows the little men as they escape through a time-portal.

Kevin and the robbers land in 18th-century Italy as Napoleon lays siege to the city of Castiglione. Having impressed Napoleon with a violent dance number, the robbers are invited to dinner, where the conqueror gets drunk and falls asleep. The robbers steal Napoleon's fortune and escape with Kevin through another time-portal.

They land in medieval England, where Randall, the robbers' leader, confides in Kevin that the fabric of the universe is far from perfect, since their ex-employer, the Supreme Being, only had seven days in which to make it. Using the map, the robbers plan to make their fortune by exploiting the many rifts in time.

In 12th Century England, their loot is confiscated by Robin Hood, who assumes they are donating it the poor. The robbers are observed by Evil, who seeks the map for himself in order to overthrow creation. Evil magically compels the robbers to seek 'the Most Fabulous Object in the World', which resides in Evil's domain, the Fortress of Ultimate Darkness. The appearance of the Supreme Being forces the robbers to flee, but Kevin runs through the wrong time-portal.

Landing in ancient Greece, Kevin inadvertently saves the life of King Agamemnon as he battles a cadaverous Minotaur. Kevin returns with the King to the city of Mycenae, where Kevin decides he wants to stay. At a court banquet, Agamemnon proclaims Kevin his son and heir. To Kevin's horror, however, the robbers appear, disguised as entertainers. They rob Agamemnon's court and kidnap Kevin under the pretence of a magic act, making their getaway through a time-portal.

Kevin and the robbers turn up on the deck of an ocean liner, where Randall tells Kevin that he has located the Most Fabulous Object in the World. Unaware that they are actually aboard the Titanic, Kevin and the robbers are left drifting in the Atlantic after the vessel sinks, along with their latest haul.

Luring them with the promise of the Most Fabulous Object, Evil draws Kevin and the robbers into the Time of Legends, where they are hauled aboard a fishing boat by a man-eating ogre, Winston, and his cannibal wife. Under the guise of treating his bad back, Kevin tricks Winston into allowing the robbers to hurl him and his wife overboard before the gang escape in the monsters' boat. The vessel runs aground on the bald head of a wading giant, until Kevin injects sleeping potion into the monster's scalp. The robbers sneak away and wander an endless beach in search of the Fortress of Ultimate Darkness, which Randall uncovers after destroying an invisible barrier.

Kevin and the robbers are lured inside the Fortress by the sight of the Most Fabulous Object. But the Object proves an illusion and Evil snatches the map. Kevin and the robbers are imprisoned in a cage suspended above an abyss, but manage to escape by making a rope and swinging across the void to safety.

Kevin confronts Evil, who is about to eviscerate the boy when the robbers arrive with reinforcements gathered from various periods in history. Having despatched the army of cowboys, archers, knights, tanks and spaceships arrayed against him, Evil is about to kill the robbers when he is himself destroyed by the Supreme Being. Manifesting in the form of a smartly dressed old gentleman, the Supreme Being reveals that He allowed the robbers to steal the map in order to test-run His latest creation: Evil.

Having been restored in their jobs, the humbled robbers depart with the Supreme Being. Kevin awakes as firemen rescue him from his burning home. A stray fragment of Evil causes Kevin's parents to explode. One of the firemen, resembling Agamemnon, winks at Kevin before departing.