For Londoner Fern King, Annwn is her second home - the dream mirror of London, the city she loves. An astonishing world, a world where Dreamers walk in their slumber, their dreams playing out all around them. And Fern, along with her twin brother Ollie, is a Knight, a trusted guardian and protector of those Dreamers - and every night is spent in Annwn, fulfilling that previously only-imagined destiny to guard those who sleep. But Fern is struggling since the loss of her extraordinary powers - and her nemesis Medraut, who seeks to control and to ruin Annwn is gaining ever more control. Annwn is a dangerous place to be for the Knights, with Dreamers recruited to be Medraut's personal army, the Knights' stronghold Tintagel starting to crumble and the last of the Fay slowly being lost. Fern, and the Knights', only hope is to retrieve Excalibur, and find the Grail - but will Fern find herself equal to this, and can she save the world she loves and see hope, imagination and wonder restored to Annwn?