This gripping adventure story is packed with eccentric characters, thrilling secrets, amazing inventions and breathtaking surprises. Sam's holiday with his friends Zara and Ben is interrupted when a bedraggled traveller blows in on a storm, reawakening a mystery from their Great Uncle Alexander's past. For thirty years, the remote Arctic island of Nordbergen has remained desolate and uninhabited. Now, strange aircraft have been seen landing and armed guards patrol the island's fringes. Professor Murdo has returned to Nordbergen to complete his secret and deadly work. Sam, Zara and Ben embark on a desperate rescue mission to the frozen Arctic Ocean. To make the journey, they must discover one of the most extraordinary secrets in the world. To survive, they must rely on their courage, their ingenuity and the assistance of strangers.

Ben, Zara, Sam, and Marcia begin their summer vacation by helping Professor Ampersand and a new friend build the Silver Turtle, a futuristic airplane, but on the day the first test flight is planned, a strange woman steals the airplane with the children inside.

A painfully shy old man has approached Professors Gadling, Gauntraker and Ampersand with an archeological find: early human remains that don't fit in with anything known to science. Soon, Sam, Zara, Ben, Marcia and Adam are joining the professors on an expedition to a remote island in South-East Asia to investigate further.