As World War II sweeps the continent and England steels itself for German attack‚ Maggie Hope‚ former secretary to Winston Churchill‚ completes her MI5 training. Spirited and strong-willed‚ with a sharp mind for mathematics and code-breaking‚ she expects to be sent abroad to gather intelligence. Instead‚ she’s dispatched to Windsor Castle to tutor Princess Elizabeth in math. Yet castle life quickly proves more dangerous than expected.