The Bell in the Fog by Lev A.C. Rosen
The Bell in the Fog is the second in the Andy Mills series and I do think it's best to read Lavender House first. It gives a good introduction to Andy and his world, along with a couple of characters who reappear here.
Andy is set up as a private detective now, but because he used to be a cop the community doesn't trust him, so he's not getting much business. He lives above Elsie's bar, the Ruby, and he's costing it business too, so she's not making enough to pay the bribes that prevent raids. He needs the money, so when someone from his past wants to hire him to find out who is behind blackmail photos that could threaten his military career, Andy takes the case.
The mystery itself is of course more complicated than it seems at first, and more dangerous. It's also so connected to Andy's past that maybe he's not seeing things as clearly as he should....