The Enterprise is sent to Goran IV after a Federation probe crashes, potentially causing a toxic gas to form in the atmosphere. The crew must determine if the primitive Goranians truly are in danger, or if the cure -- waiting for dispersal aboard the Enterprise -- will prove more harmful than the sickness. A length of tritanium wire from the smashed communicator proves useful to saw through the bolt on the door. Kirk and Spock find McCoy's cell, but are forced to escape without him.