Entomologist Niki Jumpei (Eiji Okada) misses the last bus home when exploring for insects in a series of sand dunes, and is persuaded by local villagers to spend the night in a house at the bottom of the sandpit. An unnamed young widow (Kyôko Kishida) lives there alone, forced by the villagers to dig the sand that they sell to nearby cities for construction. Enslaved to dig sand alongside the widow, Niki plots his escape even as he adapts to his imprisonment.