Biggles and Algy fight a private war with criminals and the Indonesian Army in order to protect the pearl collection of a friend of the British government. He is cut off in his forest mansion in Malaysia and asks Biggles to help get him and his pearls away from danger.

Unfortunately that proves difficult without an aeroplane. The duo are cutoff at the mansion and have to instead help prepare to repel an invasion. When Biggles finally makes a dash to collect the plane he is cutoff and captured, only to escape when Algy unknowingly blows up the kidnappers whilst removing a tree.

In the end Biggles is able to get word out, and returns with a plane and a platoon of soldiers. The bad guys are vanquished (those that are left) and the pearls are moved to a safer home, in England.

And the blue moon? That's the most impressive (and largest) pearl in Lin Seng's collection.