Professor John Ivarsson has been persuaded by Sir Anthony Ross, a wealthy Englishman, to undertake a search for Sir Anthony's son Donald, who disappeared in the Arctic. Donald left two clues: a page from an old Hudson's Bay Company journal mentioning a hidden island 'far beyond land's end where the whales go to die', and a curious map of carved whalebone. A party of men take off in the Hyperion, a giant airship. During a nerveracking flight, the captain almost falls to his death before the searchers reach Fort Conger inside the Polar Circle. And that turns out to be the start of an adventure of a lifetime.