Septimus must elude the plans of Merrin Meredith and Tertius Fume in order to find the House of Foryx, a place where all Time meets, and secure the release of Nicko and Snorri.

When, in 1931, there is a breach between this world and the Archipelago of Dreams, John and Jack, two of the Caretakers of the Imaginarium Geographica, must race through history using a time travel device left by Jules Verne, and discover the identity ofthe Cartographer.

The Winter King's Shadow, having gained control of the doors from the Keep of Time and of an army of Dragon Shadows, plans to use the turmoil of World War II to conquer worlds, but all Caretakers, past and present, come together to stop him, using some unlikely weapons.