The Earth is ready to colonize planet Ark as the initial tests showed there are no higher forms of life on it. Several ships are already on the planet preparing bases for the colonists. Androids working outside one of the ships start acting strange. Stanislaw, the communication officer, starts hearing voices of a crying baby and a call for help by a woman. In an old wreckage of a spaceship out in the mountains the crew find corpses of two people that had been dead for years. It turns out it's a ship from Earth that disappeared years ago. Soon they have an alien visitor on the ship - a boy that looks remarkably human. The colonization plans are canceled as the planet is now deemed occupied. All other ships leave the planet except for one that stays behind to establish contact. They realize the boy is a human son of the couple from the crashed ship nourished and raised by the alien civilization. But is he more alien than human? The boy learns to converse in human language in just few hours and avoids answering questions. The crew intends to use him to establish contact with the native civilization but things don't go quite the way they expect it.