Well, I finished it. But I can’t recommend it.
I didn’t realize until I searched online for a cover image – that this is the third in a series.
The authors are known for dark fantasy. I guess possession by a malevolent spirit released from a broken jar hidden for centuries in a secret room under Venice could take this into the fantasy realm, but the spirit is not actually evil, the main characters are boring, and the story is very contrived and awkward.