It's August 1952, and seven-year-old Nickel Smith spends a day at the seashore with her mother, aunt, and cousin Leroy, who is recently motherless and frightened of the world around him. As the group begins work on a magnificent sand castle, the sisters try to coax Leroy out of his shell by telling stories about their own childhood trips to the shore. But Nickel's jealous taunting of her cousin escalates, and the weight of family history between her mother and aunt rises to the surface, until a surprise attack forces them all to come together, in a life-changing lesson on family and all the pleasure and heartbreak that comes with it.