Three young men are entrusted with the Imaginarium Geographica, an atlas of fantastical places to which they travel in hopes of defeating the Winter King, whose bid for power is related to the First World War raging in the Real World.

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 of the 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.