Siblings Ofelia and Philémon are on their way home to Sweden to celebrate Christmas with their grandmother. Onboard the ferry, their father spends most of his time playing cards in the lounge, leaving the children to fend for themselves. One day, he discovers that some rats have chewed up the money kept in a box in their cabin. He then offers a reward: a coin for every rat tail the children can collect. But the clever diesel rats Lucky Closette and Don Calzone catch wind of the plan — and Lucky, who is both brave and mischievous, knows exactly how to put an end to the children's rat hunt.
