During the Second World War, young Mahito suffers a heartbreaking family tragedy and must move to the countryside, where his father works for a family that manufactures airplanes for the Japanese army. Isolated, Mahito begins to explore the mysterious landscapes around him and meets a mysterious gray heron who guides the boy to an abandoned tower. Curious, he enters the tower, and from then on the film unfolds in a marvelous and often breathtaking phantasmagoria.