It was super fun to read a mystery set in Venice that isn't written by Donna Leon! If for no other reason then to get an American viewpoint on it.
However, it has a distressingly obvious plot structure. An old friend of Mary's disappears, and the disappearance is clearly due to her relationship with her family, and specifically her relationship with her brother. Gosh, I wonder where that is going and why that relationship is fraught. Along the way to that reveal (way too late in the book), we see a number of very odd communities, such as a set of rich party-goers and a reclusive women's group. Oh, also, the real-life character Cole Porter, which was triply strange.
Anyway, because the reveal was obvious to me, the best part of the book was the portal into what Italy was like in the days before WWII, with fascism taking hold. I'd certainly never thought of what it meant for Venice - as a relaxing vacation destination - to have war thrust upon it. In that sense, Porter's inclusion made a great deal of sense. (Still off-putting to have actual living beings in a mystery series, no matter how you swing it.)