Jonathan Oliver is chasing down an intruder on Lake Oswego’s Iron Mountain when he discovers some long-buried artifacts. One of these relics sparks a remarkable spinoff from the Oliver family’s anti-gravity inventions. Together, Jon and his father incorporate their breakthrough into a revolutionary submersible design.

At the invitation of Dr. Graham MacKenzie, the Gyrosensors team travels to one of Scotland’s wildest and remotest regions-and its deepest lake-to develop their secret prototype. While staying at Dr. MacKenzie’s retreat center, they meet a pretty but mysterious Frenchwoman going under an assumed name.

Across the loch, the crusty, reclusive caretaker of a Victorian-era hunting lodge is hiding staggering secrets of his own. During the prototype’s construction and sea trials, Jon and his family confront enemies on land, in the air and under the water. In the end, Jon rekindles a love from the ashes of his youth and uncovers an ancient, holy treasure-hoard. Illustrated.