An alien named Baltazar has set his sights on Earth, planning to compress its population into diamonds. The Tenth Doctor and Martha Jones arrive on his ship, which he hand-crafted himself, to stop him. The Doctor threatens him with a spoon, which Baltazar cuts in half with his metal claw hand. The spoon happens to be made of a special fungus, which when introduced to the metal ship quickly begins to rust it. As the ship falls apart, the Doctor frees Baltazar's huge metallic bird, Caw, who carries Baltazar away. The Doctor muses that Baltazar will end up on the ice prison planet Volag-Noc at some point. Some time later, Caw takes the Doctor and Martha to his home planet, where he gives Martha a brooch as a gift. He also spits up a datachip, explaining that it and three others like it hold the location of The Infinite, an ancient spaceship that can grant people their heart's desire. Each datachip leads to the next one. At first unwilling to search for it and about to destroy the chip, the Doctor is forced to when Caw notes that Baltazar has a copy of the datachip. As the two set off on their quest, Caw is revealed to be working for Baltazar.

The Doctor comes to 1950's North America for a bowl of chili but finds himself in the middle of a secret intergalactic conflict where the military hidden in Area 51 have joined forces with an alien race to help capture one of their enemies in return for help defeating the Russians. But in a time of war-mongering and fear, who are the real monsters and who can be trusted. With waitress Cassie and her Native American friend Jimmy Stalkingwolf, the Doctor races to defuse the situation and save Earth