One minute Sam, Zara, Ben and Marcia are spending their summer with the very eccentric Professors Ampersand and Hartleigh-Broadbeam, working on an experimental airplane. They have no idea that someone has bugged the room and is listening to every word they're saying. The next minute they find a code on the back of an old photograph and start doing some detective work. "Give me that photograph, boy," says a voice, and it means business. Who can they trust, and why are these people after them? It's a great adventure with a few twists and turns. Fly along in the Silver Turtle as the children flee the hangar running for their lives. This is the sequel to The 7 Professors of the Far North by John Fardell.