The novel opens, and we're given the initial setup. It's 1942. We're on the Caribbean island of Curaçao, and World War II is under way. The island is being stalked by German submarines that arrived during the nighttime and are targeting the area's oil refineries and tankers.
We're also introduced to the protagonist, Phillip, a young schoolboy who has never seen war before. He's "not frightened, just terribly excited" (1.5). Don't worry; that will change. We also meet Phillip's father, who works for one of the oil refineries and is the reason the family relocated from Virginia to Curaçao. Phillip and his dad have always been close – unlike his relationship with his mom. She's a bit of a nervous type and (as we will find out later) kind of racist. There's also Henrik van Boven, Phillip's school friend who is Dutch and with whom he plays around the city of Willemstad, the capital of Curaçao.
The arrival of the German submarines spells trouble for Willemstad. The oil tankers are in danger and many of the sailors refuse to get on board for fear of being torpedoed and sunk. Phillip's mother wants to go back to Virginia with her son, which creates tension with Phillip's father. Once the German submarines blow up the S.S. Empire Tern, a big British tanker, she decides to leave once and for all and is determined to take Phillip with her. Phillip wants to stay on the island with his dad, but his mom books passage for him to sail with her on a ship called the S.S. Hato.
As luck would have it, the Hato is torpedoed by the Germans. Phillip is knocked out during his evacuation from the ship. When he finally comes to, he is no longer on one of the lifeboats. Instead he's on a raft with a black West Indian man with a very thick accent named Timothy and a cat named Stew Cat. Timothy builds a shelter on the raft for the two to rest under.
Timothy and Phillip don't really get along at first. For one thing, Timothy rations the water instead of letting Phillip gulp as much as he pleases. To make matters worse, Phillip loses his sight from his injury during the torpedo blast. He goes completely blind.
The man, boy, and cat drift in the sea and finally happen upon a small cay (island). Timothy steers the raft to the island, even though Phillip wants to stay at sea (better chance of rescue, he thinks). On the island Timothy builds a hut and catches langosta (lobster) for the castaways to eat. Timothy eventually reveals that the two of them are probably in an area known as the Devil's Mouth. (That doesn't sound good.) The place is rarely accessible by ship, so they realize that their only chance of rescue is that a plane might see the smoke from a signal fire.
Tensions build between Timothy and Phillip as the two attempt to live together on the island. Phillip realizes that Timothy can't spell, which causes Phillip to feel all high and mighty. Timothy, meanwhile, pushes Phillip to do tasks that he doesn't want to do (like weave sleeping mats). Eventually the situation blows up. Phillip calls Timothy ugly and stupid and Timothy smacks the bratty Phillip in the face. For some reason, this act of violence seems to knock some sense into Phillip. He realizes that Timothy is only trying to help them both survive on the island. Phillip decides he wants to be Timothy's friend and asks Timothy to call him Phillip instead of "young bahss" (9.3).
After the fight Timothy and Phillip grow closer. They talk about their backgrounds and families. Timothy makes Phillip a cane to help him get around the island, and Phillip learns how to do things like fish. Phillip even eventually climbs a big palm tree to get coconuts – a major triumph for him. Despite his blindness, Phillip is becoming more independent and empowered. Meanwhile we learn that Timothy is in poor health. One day he gets a fever, and it's Phillip who must be the protector and caregiver.
Timothy, who practices voodoo, starts to believe the island is cursed with bad luck, and he thinks that Stew Cat is the problem. Phillip worries for Stew Cat's safety, but Timothy performs a ritual that doesn't hurt the cat in the least, though it scares Phillip to death.
Around this time a tempest (hurricane) strikes the island. Timothy and Phillip prepare as best they can, but their shelter is blown away. In the end, Timothy shields Phillip from the storm with his body, while the two hold onto a rope around a palm tree. Though he lives for a few moments after the storm, Timothy eventually dies; his body is cut, bruised, and bleeding from the wind and debris. Phillip is thankful for his friend and buries him.
Soon after Timothy's death Phillip begins navigating the island alone and has a couple of adventures. He wanders into a bird nesting ground and is attacked. Then a moray eel bites his hand. A plane flies overhead once, but Phillip is unable to get the pilot's attention with the signal fire. Eventually Phillip discovers how to make black smoke using oily bundles of sea grapes. In no time he successfully flags down a plane. Success!
Phillip and Stew Cat are finally rescued and reunited with Phillip's family. An operation in New York miraculously restores Phillip's sight. The family returns to Curaçao, but Phillip's friend Henrik seems so young now that Phillip decides to hang out with the black West Indian people instead, who remind him of Timothy. As the novel ends, Phillip is studying charts of the Caribbean and dreaming of returning to the cay one day.