Nature warden Tim Corn helps to spot a rare seabird, an all-black storm petrel, off the little Isle of Lifandoy. Meanwhile terrible news reveals that Lifandoy's ownership has changed, while Tim's eccentric Uncle Wilfred has vanished down a hole and made a historic discovery, which he reveals to Tim and his fiancée Jessica Bull. But all is overshadowed when a Canadian cult, the People of White, arrive to take over the island. The cult's demands soon shock the islanders. Tim's ideological foe Graham Fytts sides with the cult, while Wilfred, Jessica's scheming small sisters Alice and Rosalind, and Darren Stocks with his beery friends all plot to evade its restrictions. The cult's members in return attempt to brainwash or convert the islanders. What might happen when the cult test Tim an Jessica's Christian beliefs? Can they still marry? Can the island be saved? Who might turn to violence? And where are those black birds?