Back To Bologna by Michael Dibdin.
This is the tenth book in the series featuring Michael Dibdin's Venetian detective Aurelio Zen. They're about as far from Hercule Poirot as you could imagine, though.
I think it was Graham Greene who used to subtitle his books "Novels" or "Entertainments", just to give the readership some idea what to expect - a similar categorisation might be useful for the Zen novels, from the properly gritty and bloody ones (though still leavened with the trademark wit and keen observation of Italian eccentricities) like Dead Lagoon and A Long Finish (these two are the absolute pinnacle of the series, for me) to the more farcical ones like Cosi Fan Tutti. Back To Bologna is very much in the latter vein, and it almost feels as if Dibdin only decided to make it a Zen novel at the last minute, as the supposed main character is hardly in it. It bowls along very entertainingly, though, for all that (or maybe because) it's pretty lightweight stuff; I zipped through it in a couple of days. I'm not sure this is the best place to start if you're new to the Zen series; you're probably better off starting at the beginning (Ratking) and working through them in order.
The non-Zen Dibdin novels are well worth checking out as well, though they're all over the place stylistically: Dirty Tricks is a hilariously black comedy (adapted rather limply for TV with Martin Clunes a little while ago) and Dark Spectre is an equally black and relentless American-set thriller - these are the two to start with. That gives you 12 books to be going on with. Don't say I never do anything for you.