The Great Train Mystery (SpongeBob SquarePants)

When Mr. Krabs gives SpongeBob the only key to the vault holding the Krabby Patty's secret recipe, SpongeBob vows to guard it with his life. But as soon as SpongeBob and Patrick board the train to get the recipe the key is mysteriously missing. Who could have stolen the key? SpongeBob and Patrick are on the case!