Bridgerton meets Agatha Christie in this dazzling third instalment to the captivating Regency-era Lady Petra Inquires mystery series.

September, 1815. Autumn is in the air as Lady Petra Forsyth and some of the most illustrious members of the ton descend upon Windsor Castle for a week of royal celebrations, with the highlight being Queen Charlotte's inaugural patisserie contest for the best bakers employed by England's finest houses. Not only is Lady Petra's own cook one of the contestants, but Her Majesty has requested that Petra herself serve as one of the judges.

Petra's happiness at tasting delicious cakes and biscuits only increases at finding her beloved Aunt Ophelia in attendance at Windsor, as well as Sir Rufus Pomeroy. As England's most famous former royal chef-turned-cookbook author, Sir Rufus is slated to present his best recipes to the Queen during the festivities, with Petra being granted an early viewing in the royal library.

Yet upon arrival, Petra instead encounters a frantic housemaid pointing to a body of one of Her Majesty's guests-and to the valet still tugging at the silk ribbon used to strangle the victim. What's more, the valet turns out to be Oliver Beecham, the ne'er-do-well brother of Petra's own lady's maid, Annie. But as Oliver is hauled away to the dungeons, he protests his innocence, claiming the late guest argued with several aristocrats, including the Prince Regent and Petra's Aunt Ophelia, and boasted about hiding a potentially scandalous document within the vastness of Windsor Castle.

When some poisoned tea meant for Petra is consumed by one of her fellow judges, it's clear the real killer is still walking the castle's halls. Indeed, in order to prove the innocence of Annie's brother and find the incriminating document, Petra will need to act like a lady, eat like a chef, and think like one of Her Majesty's best spies before a murderer can turn the celebrations from sweet to royally deadly.