Isabel Dalhousie’s debut in Alexander McCall Smith’s The Sunday Philosophy Club means that present-day Edinburgh now has a pair of rival sleuths, whose stamping grounds are as different as the city’s Old Town and New Town, yet largely occupy the same space. The genteel, rarefied world of McCall Smith’s new heroine, an amateur investigator who inherited considerable wealth, consists of concert halls, lecture theatres, art galleries, drinks parties and the delicatessen run by her niece Cat; whereas the city Ian Rankin’s veteran DI John Rebus moves through in Fleshmarket Close consists of pubs, police stations, a rundown housing estate, a detention centre for asylum-seekers, a gangster’s pad and the so-called “pubic triangle”, which is home to prostitutes and a lapdancing club. Only when Rebus visits the university, seeking a Senegalese student who reported a murder, do their respective spheres briefly touch.

Normally occupied with editing an academic journal, planning meetings of the eponymous club (which never meets in the course of the novel, despite the title) and brooding on Kant and ethical dilemmas such as whether to tell Cat her current boyfriend is odious, Dalhousie turns detective on seeing a young man fall to his death from the circle at a concert. Unconvinced that this was an accident — and feeling that the “moral proximity” of being an eyewitness makes it her duty — she first quizzes his flatmates, then explores whether he was involved in a financial scandal.

McCall Smith’s Mma Ramotswe is clearly Miss Marple transplanted to contemporary Botswana, and here too he looks back to pre-1939 detective fiction, with Dalhousie recalling Lord Peter Wimsey in her exaggeratedly privileged lifestyle, and Father Brown in mixing sleuthing and metaphysics. She too believes “people had lost their moral compass”, and that she exemplifies a life of altruism and civility that is becoming rare.

But while Precious tends merely to sigh over the ways of the world, Isabel (who can be seen as a mask from behind which the author voices his own aversions) seethes with dislikes ranging from Stockhausen to press intrusiveness. By no means just a tweedy old stick, however, she fantasises about sleeping with Cat’s former boyfriend Jamie (but realises “such thoughts were unacceptable”), so as to add sexual coaching to her tips to him on how to regain her niece.

Her charm is undeniable, and those for whom the elementary plots and small casts are part of the retro appeal of the No 1 Ladies’ Detective Agency stories will relish the similar lack of clutter here. But the new series lacks the novelty of the Botswana mysteries’ setting, standing or falling by whether you find the inside of Dalhousie’s head an enjoyable place to spend an entire novel; and in The Sunday Philosophy Club it comes to feel at once airless and exhausting, with McCall Smith’s donnish heroine prone to turn every experience into a cue for either fogeyish grouching or a philosophical pensée.

Rankin has often uncovered venality and latent violence behind the Dr Jekyll-like respectable façade of Edinburgh’s professional classes, as Dalhousie does in her first outing, but in Fleshmarket Close he concentrates instead on the city’s social underbelly. Rebus is part of a team hunting for whoever stabbed a Kurdish journalist to death, and his characteristically semi-detached investigation takes in a racket combining people-smuggling with illicit subletting of council flats, cockle-pickers at nearby Cramond, inflammatory tabloid journalism, prickly encounters with an immigration officer and regular visits to an Immigration Removal Centre.

These chapters display Rankin at his best, recalling Dickens both in the vigour and ambition of their social portraiture and in their campaigning thrust. Like much of his recent work, however, Fleshmarket Close jumps to and fro between Rebus and his protégée DS Siobhan Clarke, who searches for a rape victim’s missing sister and is later involved in a murder inquiry. Such is the strength of the sections on refugees that you soon find yourself resenting this second plot as an irksome distraction; a humdrum crime novel, it’s hard not to feel, has been needlessly spliced into an outstanding one.

THE SUNDAY PHILOSOPHY CLUB by Alexander McCall
Smith Little, Brown £14.99 pp281

FLESHMARKET CLOSE by Ian Rankin
Orion £17.99 pp416

Available at the Sunday Times Books First price of £11.99 and £14.39 (Rankin) plus £2.25 p&p on 0870 165 8585

Explore Books

• Book Extracts

• Book Reviews

• Books Group

• Audio Books

Times Recommends

• The 100 Best Books of the Decade
• The Times picks the 50 best paperbacks of 2009
• The conversation: James Ellroy