On the planet Sabra in the ocean special. Earthling stations extract rare metals from local shells - radium, tantalum, rhenium. The natives, the intelligent dekabrakhs (ten-armed creatures), contain a lot of niobium. Their mass slaughter begins. The Deca civilization is biological. They have living tools: slaves - arrows, monitors with grasping tentacles, corals growing in the desired shapes. They communicate with each other only empathically - “do as I do.” (And since they are all the same, this communication is good). People come up with special things for them. language based on different positions of the tentacle arms.