The team from NWIDI is at it again! This time, a trip to southern Japan to investigate a mysterious underwater pyramid off the coast of Yonaguni Island involves the four friends in a case of murder and international kidnapping. The maiden voyage of the team's newly acquired Learjet begins with a dramatic landing in Alaska's Aleutian Islands and, after a run-in with the Department of Justice in Tokyo, the team begins to think they should never have left home. When they finally touch down on Yonaguni, a Japanese-American exchange student befriends them and helps them get to know the tiny island of 1,200 people - and the dark secret being protected there. A tsubute discovered outside the NWIDI headquarters in Seattle reappears on Yonaguni and leads the team to a startling discovery about the true nature of the island and its original inhabitants. [A tsubute is an ancient Ninja throwing weapon.]