This should really get four stars, but it's nothing special.
Except, that is, in the overcrowded and ridiculously bottom-heavy field of Mysteries, which are lately more and more populated with idiot schemes for plots, cutsie/impossible detectives, cringeworthy dialogue, and freshman-year-poetry style mishaps.
It has become really difficult to find Mysteries that have no "close-the-cover-and-stand-away-from-the-book" moments, the point where all the telltale signs converge to prove they were not mistaken, the page where you lose a little faith in yourself for having come this far in pursuit of what's rapidly translating itself into The Stupid.
One symptom of this epidemic is the can-you-top-this competition wherein any newly written murder must be somehow more spectacularly grisly and uncannily gross than whatever is in current bestsellers. (If you're writing mysteries and you really think it's about that, you've got a lot to learn. Start with Aeschylus, work your way forward in time. Pause, reboot with Edgar Allen Poe. It's what you don't show that really tweaks them out, dude.)
Even voiding and ignoring those grand mal kinds of experiences, there's often enough some little nag that means you won't be returning to an author, and won't be recommending the present volume either. Any 'catchword' or repeated expression, a sidekick who is a little too gullible, a woman detective in front of whom entire gangs of construction workers cower, a character who is just in the plot to be funny, and, unless un-named and deep in the background, any pet anything. Trade you two grouchy superintendents for a story that has no nicknames involved...
So the need to consume as many good Mysteries as possible is balanced by the desire to get snagged by the fewest 'drawback' ones, with reading time being finite and all... It's always great to find an un-showy, un-remarkably functional mystery, that is free of all the negatives.
It's not the same as fiction, or, say literature, where a work has to score high into the positives on all counts, as well as being original. Mystery simply has to function properly for what it is, which is genre excercise in a pre-existing subset, of which there are only a few, such as Procedural, Society, Psych, Cozy, Manorhouse, Locked-Room, etc. What's required is simply avoiding those land-mines, like the temptation, for example, to have the detective always saying or worse, wearing some signature item or other. Or whistling.
It's going to sound like faint praise after all that, but Magdalen Nabb and her conscientious detective Guarnaccia avoid all the negatives and put the right positives on the scoreboard (and in the right order). But it's true. The Florence locale is concrete and believable, the characters real, and the crimes are not hyped to compete with Cormack McCarthy or James Ellroy or Hannibal Lector.
What's almost as important for the voracious Mystery reader is that when there is a find, there are more. And there are-- this is 13 in a series of 13, so a clean dozen elsewhere to feed the beastly addiction. The game, as always, is afoot.