As World War II sweeps the continent and England steels itself against German attack, Maggie Hope, former secretary to Prime Minister Winston Churchill, completes her training to become a spy for MI-5. She fully expects to be sent abroad to gather intelligence for the British front. Instead, to her great disappointment, she is dispatched to go undercover at Windsor Castle, where she will tutor the young Princess Elizabeth in math. Yet castle life quickly proves more dangerous--and deadly--than Maggie ever expected.