Commodore Rex Clive leads the Adjutant Speed Lansing and the Space Rangers through the narrow pass between the Sun and Mercury, attempting to discover the hijackers there. The passage is taken by space freighters as the best option to get to Mars at distant spots in its orbit. They discover an "old space comber" named Shangor and his motley crew of space pirates are based on Mercury. Their ships are coated with Thermallium, the only metal able to withstand the intense heat on Mercury. The Space Rangers defeat Shangor's pirates and arrests him.