First published 1935, in this edition 1941, reprint 1951. pp. 256 #280824

Whilst celebrating Ginger’s award of his pilot’s licence, an SOS on B.B.C. radio asks for Major James Bigglesworth to contact his Uncle, Professor Richard Bigglesworth. This is of course, Dickpa, previously seen in the story ‘The Cruise of the Condor’. Visiting Dickpa at his house, they find him and his friend Lord Roger Maltenham, under attack from mysterious enemies. Both Dickpa and Maltenham have returned from the heart of Western China on the borders by Tibet and have a strange tale to tell. Maltenham agrees to finance an expedition back to the borders of Tibet in search of the so-called ‘Mountain of Light’. Buying a Gannet amphibian and naming it the Explorer, Biggles, Algy, Ginger, Dickpa and ‘Malty’ fly to Tibet. On their first night, they are able to see a shining blue mountain, the effect being caused by the tremendous quantity of radium in the mountain. Attempts to approach the mountain are initially thwarted by a strange paralysing effect and giant man-eating centipedes. However, the rescue of a Scotsman called Angus McAllister gives our heroes vital information. A strange race of Chinamen called the Chungs has been holding McAllister captive. The radium in the mountain has given the Chungs weird powers, including the ability to make themselves invisible! McAllister was the Chief Engineer on a ship, captured and forced to work for the Chungs. The Chungs have the ability to use a bizarre blue ray that has a paralysing effect. However, there is an insulating fluid, which can be used to ward off its effects. The Chungs plan to invade the world from the Mountain of Light, which is their power base. The Chungs attack Biggles and the others by blue rays at their aircraft from a nearby plateau. Biggles and Ginger make a desperate journey to attack the Chungs and prevent this continuing. The Chungs then attack the aircraft in force and capture Dickpa, Malty and McAllister. Algy manages to escape and join Biggles and Ginger. Meanwhile Biggles has taken a hostage, a Chung called Prince Sing Hi and he is able to exchange the Prince for Dickpa, Malty and McAllister. An expedition to get some radium from the Mountain of Light sees Biggles falling into a network of tunnels, which honeycomb the Mountain. Biggles comes up with an idea to flood the gorge where the Chungs have their City and he is able to breach their dam resulting in a deluge of water. Back in England, the small amount of radium they recovered is found to be worth £250,000 and Malty gives Biggles the Explorer and agrees to finance his next trip.