Nick Nelson of the Space Patrol and his Martian gunner, Kodi, investigate space piracy near Mercury. The Interplanetary Express X-65 lands on Mercury on the precipice of a volcanic crater. The X-65 carries a monthly cargo of green diamonds from Mercury. The X-65 falls into the crater and is rendered useless. Going inside, Nick Nelson and Kodi encounters the Mercurian behind the crime and the Mercurian Mole Men he uses as lackeys. The Mercurian is wearing the uniform of the X-65's pilot, determining the Mercurian is guilty of robbing and destroying the ship.