Meet Huxley, an irrepressible koala with BIG ideas, and his best friend, Flapjack, a rather jumpy penguin. Flapjack would rather stay at home, but for Huxley, each new day sparkles with possibility and the chance of adventure! Huxley and Flapjack are enjoying a trip to the seaside when they meet Whizz, who invites them aboard his submarine to search for the shipwreck of the Isabella. Huxley's excited to go deep-sea diving - he's sure there'll be treasure to find - but Flapjack can't help worrying. What if something BIG and FISHY finds them first.