In the 27th novel of this new series, Tom is now back from his adventure on Neptune and had a small mission to accomplish before he feels the previous one is complete. His small unmanned test submarine was lost on its deep sea test in the region of the Mariana Trench south of Guam, and now he wants to go get it back. Nothing is as easy os it sounds, and he must find a way to get Yamato II down to Earth before it can be used.Even when he succeeds (and you just know he will) what he finds deep under the Pacific Ocean will change his way of looking at the world.But, dare he reveal what he and his small crew encounter? Or, could it cause a frenzy of activity from many seafaring nations to try to get down to see what it is for themselves?But first, he must get his new space submarine, the Yamato II, back to Earth so it can be used at the incredible depths he intends to get down to.