Seven years after facing the Dragon Shadows, John, Jack, and Charles return to the Archipelago of Dreams but their reunion with old friends is spoiled by the threat of primordial Shadow Echthroi and the apparent splintering of Time itself, and they set out on a new quest in which success and failure each carry a high cost.

With the Archipelago of Dreams in the hands of the Echthroi and the link to the Summer Country lost, the Grail child, Rose Dyson, the new Cartographer, Edmund McGee, and the Caretakers Emeritus seek to rebuild the Keep of Time but face a terrible new enemy who was once an ally.