This is the third in the series of Ms Diener’s loosely connected romantic mysteries set in the Regency period and, as with the other two, it takes as its starting point an actual historical event – in this case the assassination of Spencer Perceval, the British Prime Minister, in 1812.

The whole of society knows that James, Duke of Wittaker, is a wastrel and reprobate, a young man given to drinking, wenching, and gaming who was a sore trial to his late, upstanding father. What the whole of society does not know is that Wittaker is nothing of the sort, and that his image is just that, a carefully cultivated persona he adopted when asked – by his father – to engage in undercover activities on behalf of the Home Office. James’ age and rank made him ideally placed to be able to move easily among the ton and to gather information on any number of the dissolute, disaffected noblemen peopling the gentlemen’s clubs and gaming houses.

But so long spent indulging in a debauched lifestyle have adverse effects on James, whose persona became less of a persona and more of a reality – until a horrific wake-up call a few weeks before the beginning of this novel makes him decide to get out so that he can live his own life.

Miss Phoebe Hillier lives in a state of almost constant irritation and frustration with the strictures imposed upon her by society. She is betrothed to Lord Sheldrake, an engagement engineered by her father to make a marchioness of his daughter in return for her very large dowry and estates. When Sheldrake suddenly breaks off their engagement and tells her of his intention to flee the country, Phoebe is relieved – but is left on the brink of social ruin.

A couple of days later, the Prime Minister is assassinated, and some of the things Sheldrake had said to Phoebe on the occasion of their last meeting begin to make her suspicious – but she can’t quite pinpoint either why or of what. Then, when the Duke of Wittaker turns up unexpectedly at her home, she remembers Sheldrake’s offhand comments about his departure ensuring her safety, and her suspicious come back with a vengeance – could Wittaker be one of the men from whom Sheldrake was fleeing?

James has, in fact, been asked to slip back into his old role in order to gather as much intelligence about the situation as he can. Many people, including those among the highest echelons of society, had no love for Perceval, and he is tasked with keeping his ear to the ground and using his reputation as a congenial fellow in sympathy for the disaffected to loosen tongues and elicit information which, he knows, “was easier to come by if everyone thought he was drunk.”

To say more about the plot would be to give too much away, so I’ll just say that Ms Diener has very cleverly taken the historical facts of the assassination and the subsequent prosecution and conviction of the suspect, and interwoven them with her own theories and interpretations of events, which are in themselves quite fascinating. In her comprehensive Author’s Note, she separates fact from fiction and, shows how she has arrived at the conclusions drawn by her characters, and her version of events is just as plausible as any of the other theories she mentions.

James and Phoebe are engaging characters who are thrown together because of the investigation and also drawn together on a personal level. When Phoebe is targeted by would-be assassins, James charges himself with her protection; and it’s a relief to find an intelligent and independently-minded heroine who doesn’t feel the need to throw herself into the path of danger at every available opportunity. She isn’t a simpering miss, but sees the sense of the advice Wittaker gives her about ensuring her personal safety. Most importantly, however, Phoebe is both surprised and gratified that the duke doesn’t talk down to her or view her as being of lesser import or intelligence. Her father and fiancé had condescended and underestimated her, whereas James listens to her ideas and lets her participate in his investigation when it is appropriate for her to do so.

This is a novel in which the romantic aspects of the story take second place to the mystery, and because of the time-frame (the historical events described take place in less than a week), the romance does feel a little rushed. But that said, it reaches a satisfactory conclusion, and the low-key nature of it was a welcome relief from the overkill of mental lusting that is characteristic of so many romances these days.

A Dangerous Madness is well-paced, meticulously researched, and easy to get into without being overly simplistic. There are a few turns of phrase which feel a little anachronistic, but for the most part, Ms Diener recreates the period very well, with particular emphasis on the uncertain political situation of the time.