Dandy Gilver and the Proper Treatment of Bloodstains, By Catriona McPherson

In the bar of the House of Commons, you'll find MPs from both sides happily quaffing together, with none of the animosity one might expect. But such a collegiate atmosphere isn't present at crime-fiction conventions when two types rub shoulders. The writers of tough urban crime tend to gravitate together, while those who specialise in less sanguinary Home Counties mysteries – the "cosies" – tend to keep to their own. Of course, there are exceptions: Val McDermid may plumb the most gruesome reaches of psychopathology, but she's a passionate Agatha Christie aficionado.

What would McDermid make of Catriona McPherson's novel, which appears to be firmly in the cosy camp – but is it? The Dandy Gilver series demonstrates the author's faultless assimilation of this idiom. A genteel note is sounded throughout, with the middle-class Dandy, an amateur female sleuth in the 1920s, solving knotty mysteries. But there's a subtle detonation of the cosy genre, as the books soothe the reader while clandestinely taking on more serious concerns.

McPherson's latest is possibly the most radical in that sense, dealing with the politicisation of the serving classes under cover of a murder-the-wife plot owing not a little to Patrick Hamilton's Gaslight. Nervous Mrs Balfour has a new maid who is not all she seems. She is, in fact, a disguised Dandy Gilver, hired by the wife to protect her from the murderous designs of her husband. But can Dandy foil this bit of domestic malfeasance?

The tactics here include an acute sense of period, sharp observation of the mores of the day (both above and below stairs), a nicely-judged infusion of humour and a winning heroine. All this is "cosy" enough, but Dandy's acid disapproval of the social upheavals in letters to her husband is not necessarily shared by her creator. It's this meshing of gears that adds a piquancy to the untroubled surface of the novel.