Beechwood, the private island that Harris Sinclair owns near Martha’s Vineyard, and where he and his family spend their summers, symbolizes the family’s insularity, which Harris is largely responsible for. Literally separated from the rest of the world by water, the island is a world unto itself and represents a refuge for the Sinclair family. In addition, spending each summer on the island allows the family to further isolate themselves from the outside world, keeping strangers at a distance and ensuring that Harris has some degree of control over who comes into the inner circle of the Sinclair family.
The island is also a clear symbol of the Sinclair family’s immense wealth: one summer, Gat wonders out loud how it is possible that one person can actually own an island. Cady, Johnny, and Mirren have hardly given any thought to this question, as if this option were available to just about anyone. After the fire takes the lives of Gat, Johnny, and Mirren, Harris declines to have the police come to the island to investigate and is very careful about what details of the tragedy are released to the press—once more, he uses Beechwood Island as a means to maintain the private, insular nature of the Sinclair family.