'The Isle of Devon' is a settlement founded by Protestant refugees in the seventeenth century, on a remote island. Jonathan Standing is the son of the community's leader, Jason, and the great-grandson of its founder, Simeon. Jason finds him with a married woman and charges them with adultery. Jonathan is seized; the woman tries to swim away but is killed by piranhas.
In a hall that serves as a church and lawcourt, under a huge statue of Simeon, Jason sentences Jonathan to 15 years' hard labour. At the penal colony, an overseer singles Jonathan out for particularly harsh treatment, but he manages to escape.
Pirates discover Jonathan and take him to their captain, Laroche. Laroche, who has heard stories of the settlers' treasure, says he needs an island where his men can stay. He promises he will help restore justice to the settlement if Jonathan guides him there.
The pirates reach a farm on the settlement's outskirts, owned by the Blackthornes. Blackthorne tries to defend his wife and daughter but is knifed. Standing realises Laroche has lied to him: the pirates tie him up.
Word of the pirates reaches the settlement. Jason orders all children taken to the hall and all men to take up firing positions on the settlement's walls. Laroche tells Jonathan the islanders must surrender, as otherwise they can expect no mercy. Beneath the parapet, Jonathan tries to persuade his father, but an islander fires at him, and the pirates attack.
Pirates manage to scale the walls, enter the hall and start dragging out children and women as hostages. The islanders cease firing; Laroche enters the settlement unopposed. Jason tells Laroche there is no treasure. Laroche disbelieves him. He announces that for each day the islanders remain silent about it, two of them will hang.
That night, while the pirates carouse drunkenly inside the hall, Jonathan's friend Henry unties him. He tells him the treasure does exist: his own father told him, just before he died, that the original settlers brought gold with them, but only Jason knows where it's hidden.
Henry and other islanders grab arms and horses, and ride away. Jonathan stays and bars the settlement's entrance behind them. Hearing the noise, Laroche rushes outside. He reminds Jonathan what will happen if he is not told where the treasure is. Jonathan pleads with his father, but Jason is obstinate; he points to the statue and asks Jonathan what Simeon would do. Jonathan, saddened, turns away to see that Laroche is watching them.
Laroche gathers everyone in the hall, saying he has 'made a discovery'. He orders his men to remove the statue. Breaking up the boards underneath, they start digging but eventually strike rock without finding anything. Laroche orders the ship's mate, Hench, to massacre everyone, but Jonathan realises the statue itself is golden and shows that it has been painted. Laroche has the pirates move it out on a wagon, bringing the two Standings as hostages.
The pirates and their captives move the wagon laboriously towards a river. Henry's renegades ambush them: Jonathan escapes, but Jason will not abandon the statue. Their numbers depleted, the pirates encounter a pit the renegades have dug; their foremost two men fall onto stakes. Aware more traps are to come, Laroche orders the statue to be carried by hand, with Jason in front. As the pirates make their way through a forest, Jonathan fells a tree on them; they scatter, but one of them is crushed. Hench warns Laroche that the men will not go on. Laroche says contemptuously they cannot go back: once they reach the river, they will build a raft and transport the statue to their ship.
At the river, a mutiny breaks out. Hench disarms Laroche, saying they'll leave without him. Islanders creep up on the pirates as they tie the statue to their raft. A gunfight ensues. The remaining pirates try to escape on the raft but Jason swims up and attacks them single-handedly. Hench fights with Henry, who gets wounded but kills him; Jonathan fights Laroche, and runs him through. Piranhas swarm towards the raft and kill all the survivors, including Jason. Jonathan helps Henry away, as the statue sinks.
The pirates, believing the statue in the hall hides the treasure, order its removal. The statue is revealed to be golden beneath the paint, prompting the pirates and their captives to move it out on a wagon.
The climax centers on the revelation that the settlement's supposedly humble statue is actually the golden treasure the pirates have been seeking. The pirates' greed and violence upend the islanders' way of life, and the fate of both the colonists and the invaders hinges on this final act of unmasking. The ending underscores themes of hidden value and the destructive nature of obsession.