When twelve-year-old Katherine Howard comes to live in the Duchess of Norfolk's household, poor relation Cat Tilney is deeply suspicious of her. The two girls couldn't be more different: Cat, watchful and ambitious; Katherine, interested only in clothes and boys. Their companions are in thrall to Katherine, but it's Cat in whom Katherine confides and, despite herself, Cat is drawn to her.

Summoned to court at seventeen, Katherine leaves Cat in the company of her ex-lover, Francis, and the two begin their own, much more serious, love affair. Within months, the king has set aside his Dutch wife Anne for Katherine. The future seems assured for the new queen and her maid-in-waiting, although Cat would feel more confident if Katherine hadn't embarked on an affair with one of the king's favoured attendants, Thomas Culpeper.

However, for a blissful year and a half, it seems that Katherine can have everything she wants. But then allegations are made about her girlhood love affairs. Desperately frightened, Katherine recounts a version of events which implicates Francis but which Cat knows to be a lie. With Francis in the Tower, Cat alone knows the whole truth of Queen Katherine Howard - but if she tells, Katherine will die.