Danger, mystery, and high adventure await as Cruz boards the Explorer Academy ship on a dangerous mission to the icy north in search of the first piece of his mother's hidden cypher.In the exciting follow-up to The Nebula Secret in the Explorer Academy series, Cruz, Sailor, and Emmett, along with their new ally Bryndis, embark on their first globe-trotting mission aboard the ship Orion. Cruz jumps right back into school and starts using the latest technology in submersible underwater dives, but is soon reminded of the danger he's in when someone tampers with his diving helmet and he almost drowns. Determined to keep his eyes on the prize, Cruz sneaks away to try to find answers, but unknowingly lures his friends into bigger trouble. When a friend of Cruz's mom meets an untimely end, Cruz's luck really seems about to run out. Who is following him? And why?This captivating follow-up to book one is the sequel every Explorer Academy fan is waiting to read!