The crew race for Ape Island, using every bit of Roger’s navigation skill and Erik’s maritime nouse, and manage to reach a hidden inlet before the Murder Circus’ ship. Following Jawbone Jack’s map, they navigate the island, watched all the while by every variety of ape and monkey found there.
Eventually they come to a lake at the foot of a mountain, with a building rising from its side – an ancient observatory carved from black stone. When they venture into the observatory, they trigger a trap, and Farn and Pete are separated from the rest of the crew. Before they can find a way to rejoin the others, Farn rips away his magical disguise to reveal that he’s actually Dr Mirablis- he paralyses Pete with magic and drags him off towards the building’s centre.
The real Farn wakes up, bound and gagged in the hold of the Circus’ ship – he escapes and runs through the jungle, guided by his ghoulish senses to rejoin the rest of the crew as they wander the observatory, fighting off cultists and the terrifying form of Orcus, now with Charlie Chuckles’ severed-yet-still-laughing head stitched crudely to his chest.
In the centre of the ancient ruin, a giant ghostly gorilla guards an altar underneath a basalt orrery. Mirablis places Pete on the altar, and the building rumbles – it’s built on a dormant volcano that’s returning to life! Everything has aligned, Mirablis tells Pete – he lured him here to this island as the stars were coming into their right arrangement, and once he sacrifices Pete, the cult’s dread master will rise from Hell!
Before the sacrifice can be made, the rest of the crew burst in and a brawl breaks out, even as a lava-filled rift in the earth splits the chamber in half. With Mirablis distracted, Erik frees Pete from the altar and lies down in his place – the mystical star tattoos that Estrella marked him with disrupt the ritual, stopping the dark powers from rising! Before Mirablis can hatch some new plot, Pete tackles him down into the rift, giving his life to take revenge on his grandmother’s murderer. The observatory shakes, but the way out is barred by Orcus – and Jobu too makes the ultimate sacrifice, grappling the unkillable monster and dragging it down into the lava rift.
The remaining crew make it outside just as the observatory breaks apart and collapses into the lake. They return to the inlet to find both The Travelling Lady and the Circus’ ship – now their ship, along with whatever artifacts and treasures it holds. They sail away from Ape Island, giving Pete’s peg-leg and Jobu’s whaling spear a symbolic burial at sea, and head back to Freeport to seek new fortunes.