(To Shield the Queen is apparently the title of this novel in the US. It was originally published in the UK as The Robsart Mystery.)
The Queen, Elizabeth I, is in love. And the man she is in love with is the unpopular – and already married! – Robert Dudley. If somehow he were to get an anullment and Elizabeth married him and he assumed the role of pseudo-king, there could be civil war. Especially as Mary Stuart, ex-Queen of France by marriage and Queen of Scotland by right, is considered by many people to be the rightful Queen of England. She is the legitimate granddaughter of Henry VII of England, whereas Elizabeth, in the eyes of many, is illegitimate, a bastard, the daughter of Ann Boleyn, whose marriage to Henry VIII was never legal as he had not been granted an anullment of his previous marriage by the Pope.
But of course, the real point was that Mary was a Catholic, whereas Elizabeth was a Protestant. The civil war would be a religious war.
And then, in September 1560, Robert Dudley's wife Amy Robsart is found lying with a broken neck at the foot of the staircase in their house. Was it murder – as many suspect? Murder instigated by Dudley – or even by the Queen herself?
Enter a young sleuth, Ursula Blanchard, brought up Cinderella-style by her sadistic aunt and uncle, then widowed young after a runaway marriage, and now trying to support her daughter and herself in a very harsh world. Her mother had been one of Ann Boleyn's ladies-in-waiting, and had got herself pregnant and borne the illegitimate Ursula, then died. But now Ursula is offered a post at the court of Elizabeth, who shows a not unnatural sympathy with any who knew and loved her mother, as Ursula's mother had. They are in fact almost exactly the same age.
I won't tell you the story, but of course it is Ursula who unravels the mystery, and at the same time uncovers a widespread Catholic plot against the Queen – in which it turns out her new, sexy, half-French lover, Matthew de la Roche, is involved. Now where do her loyalties lie?