The Infinity Quest - S0.E1

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.