The 10-year-old boy Maximillian Dubois arrives home to find his Uncle Pierre's boss, Captain Horatio Murky, waiting for him with another crew member. Murky tells Max he has to go with him without even telling his mother. Murky says he will text her. They go by bus to the port of Le Havre in France where Murky's ship, the MV Ghastly, is waiting.
Murky demands Max must help him as it was Max who gave Uncle Pierre an app that enabled him to disarm all the alarms at the Louvre and steal the Mona Lisa. Pierre had been caught after stopping for food and leaving the Mona Lisa sticking out of the top of his convertible car and was now imprisoned on the notorious Devil's Island in South America.
Max is made to work and is seasick too. He then learns that they are first going to the Arctic to catch polar bears to sell. They travel to Baffin Island. Max is horrified when the crew discuss killing whales and resolves to help any animals he can.
Max has left aboard while the crew go to catch animals, and they return with polar bears, arctic foxes and an Arctic wolf in cages, together with two reindeer who were captured to use for food on their journey. Max releases the wolf in South America.
The MV Ghastly sets sail and Murky says he is doing the animals a favour as the ice is melting anyway, and he'll make lots of money and be honoured by the Queen.
Max has always been able to talk to animals. One polar bear, Dorothy, gives birth to two cubs, Little Harald and his sister Iggy. Max gets them some fish from the galley fridge. Max agrees to let them out of the cage at night if they promise not to attack the reindeer, and puts them back in the morning.
They travel to Devil's Island as Murky needs Uncle Pierre to help him sell the animals. They release Uncle Pierre, who now wants to be known as Peregrine Bubble.
They travel to Antarctica and get stuck in ice. Pierre and Murky want the animals kept in their cages but Max waits until nightfall and lets out all the animals, who escape ashore. Max goes with them and stays with Dorothy and her cubs.
After meeting lots of new friends in the Antarctic, Max has to rescue Little Harald the snow bear who gets lost in a blizzard.
In the end, luckily, a British Royal Navy frigate comes along and stops the Ghastly, to inspect their freight. Max tells the Royal Navy captain what has happened and that all the animals have been kidnapped, and Murky and his crewman Cartwright Diesel are arrested. They are found guilty of animal theft and being climate criminals, and taken back to England and put in the Tower. The animals are taken back to the Arctic. Max's Uncle Pierre escapes by hiding in the lifeboat on the Ghastly.
After a happy ending, Max arrives back in France feels his experience has made him a better person.
