'Prime Minister Churchill, the Witches of Britain are at your service . . .'

1940, and war rages across Europe. The future looks bleak. But now, emerging from the shadows, the Royal Academy of Witches offers its help. And so it is tasked with finding an ancient artefact that, were it to fall into Nazi hands, would help Hitler fulfil his twisted Aryan dream . . .

Stubborn, plain-spoken and from an unimpressive family, Lydia Polk never expected to be chosen to work under Isadora Goode, the Grand Mistress of the Royal Academy of Witches.

Now, three years into her apprenticeship, and with Hitler's armies rampaging across Europe, the Witches of Britain have joined the war effort - but not without some resistance from within, the British government having originally forced the witches into hiding.

As Lydia's power grows, she too joins the cause, tracking down magical relics in order to keep them out of Nazi hands. But a Nazi witch infiltrates the Academy with heart-breaking consequences and suddenly Lydia's mission becomes even more urgent . . . Somewhere out there, hidden amidst the chaos of war, is the Grimorium Bellum - an ancient book that Hitler craves, a book so steeped in dark magic that it has the power to wipe out civilisations - an artefact that Lydia must find and secure at all costs.

Dropped into the heart of Occupied France, Lydia finds allies in Rebecca Gagne, a French resistance fighter with a secret, and Henry Boudreaux, a Haitian-American art historian who seems to possess a little magic of his own. But tracking down this book is only half the battle - for the Grimorium Bellum seems to have a dark agenda all of its own . . .