A Death in Diamonds (Her Majesty the Queen Investigates, #4) by S.J. Bennett

Two murders in Chelsea plague amateur detective Queen Elizabeth II in the fourth book in the charming series, perfect for fans of Rhys Bowen and Jacqueline Winspear.

1957, England. Young Queen Elizabeth II is finding her way in postwar Europe, trying to repair friendships with foreign governments. Advised by her father's old courtiers, the Queen suspects that they may not have her best interests at heart. One of them is trying to sabotage her public appearances: that much she is sure of.

When two bodies turn up in Chelsea, the Queen finds herself unwillingly used as the alibi for somebody very close to her. With the reputation of the monarchy at stake, Elizabeth knows she can't face these challenges alone. She needs support from someone she can trust. Therefore, she enlists the help of an ex-code breaker, Joan McGraw, to uncover the truth.

But as Elizabeth and Joan are uncovering secrets from the past, the clock is ticking, and they are in more danger than they know.