In Biggles Delivers the Goods, Prince Lalla was the son of Major Marling and an Indian princess. Lalla had been out and so escaped capture during the first Japanese raid on Shansie, Marling's estate. He met up with Biggles and Li Chi who were approaching up the river to Shansie. Together they planned a counter attack to eliminate and free Marling. Lalla's contribution here was pivotal as he was able to summon Marling's workers to join the battle with a whistle at a crucial moment so much so that Biggles was able to leave the fighting largely to Lalla and his men. As Li Chi described it, "The Japs have lost their leader; the Shansians have found one."
Later, when the Japanese overran Shansie with paratroops, Lalla escaped to the coast with Melong, Marling's overseer. There they obtained a native kabang and sailed for Elephant Island to bring the news to Biggles. Lalla joined Biggles in his raid on Victoria Point to free Algy. Lalla managed to free his father as well--he had also been taken prisoner and locked up at Victoria Point.
At the end of the book, Lalla left Elephant Island with Biggles and his squadron. His father had given him permission to join the R.A.F.