In the seventeenth book in the Wallace Boys series, Nigel and Bruce arrive in Singapore in South-East Asia, having sailed nearly halfway round the world in the Silver Spray. They meet up with two Singaporeans, Kheng Peng, a Chinese boy, and Zainal, a Malay. A radio mayday message, in Kheng Peng's possession, from a Japanese ship in the closing stages of the Pacific War together with a visit to a former fighter of the Japanese in the famous Malayan stay-behind Force 136 lead the boys to realize they are on the trail of adventure; namely, General Yamashita (the 'Tiger of Malaya') Tomoyuki's legendary treasure.Their trail takes them to a small island, Pulau Tulai, near Malaysia's Pulau Tioman where they find more clues to the location of the treasure - and they find these clues under an unexploded World War Two bomb! Following an intensive scuba-diving course for the two Singaporeans, the boys set sail across the South China Sea.