George Barnard's life is turned upside down when she and her cousins embark on a treasure hunt. Soon, they find themselves battling a merciless enemy who wants to change the world.

When Uncle Quentin's life's work is stolen from Kirrin Cottage, the Famous Five take the night train to Scotland and are drawn into a deadly game of espionage, theft and deceit.

As the summer comes to an end, George sets in motion a final adventure to protect a circus magician from an unscrupulous doctor who wishes to make use of his powers in the clinic.