As we noted in our "In a Nutshell" section, The Cay is an amazingly awesome mash-up of a harrowing war story and a desert-island survival tale. The first few chapters focus primarily on the World War II aspects of the story, then the novel shifts genre and is dedicated to island time. Both halves are action packed.
The Cay is also a children's novel through and through, in that it explores coming-of-age themes. We see this focus in the growth and maturation of our 11-year-old protagonist Phillip.