Aliens from the Hydra constellation suffered a disaster and found themselves trapped in the mountains on the island of Sardinia. The eminent scientist Salmi, his daughter, several young people, and a couple of Eastern spies became hostages of the aliens, who needed their brains and hands to repair and control the ship. The ship takes off successfully, but the humans rebel against the three aliens, causing the ship to veer off course and get caught in a photon storm.