Convinced that his father, who had disappeared in the ocean two years earlier, is still alive, the 12-year-old Felix sets out to find him in the company of old Tom, a retired sailor, Quack, the one-legged pickpocketing parrot and Ulysses the cat, who behaves like a dog. Their journey takes them to the Isle of Eternal Night, to an underground city where a secret society is hiding led by the megalomaniac Morgäa, holder of a treasure.