Meh. The last of this series I'll read.
The worst problem here is, in part, a problem of writing mystery series about non-professionals, detectives who aren't cops or PIs, and I feel for the author, having to solve this problem. What motivates the protagonist to hunt down the answers, to put his life at risk, to spend money chasing down leads? There are really no good answers to this after a first novel. At worst, you end up with the Murder She Wrote syndrome, where everyone in some tiny town or who has ever known the detective gets killed, kidnapped, threatened, or commits murder. Here, the sober (but hardly recovered) kinda dumb-ox protagonist has some weird code about helping out anyone who was ever once at this particular AA meeting, no matter the costs.
But it's hard to buy into that code/excuse, so he really isn't well motivated from the beginning and he totally screws up his life to pursue the mystery, and it makes him terribly unlikable. I suppose you could say, well, he's a drunk, and drunks are great at self-destruction and detonating the lives of those who allow a drunk close, but it's not a very positive thing, not a compelling reason for this reader to care about his pursuance of what is clearly, from all angles, a very bad idea. At many points, he should have clearly called the detective working the case or walked away, and he makes the very worst choice over and over again. Moreover, all the people he screws over and puts at risk forgive him and are still his friends, which makes them seem like idiots, too. So it's hard to like anybody. Even the cats in this novel are irritating. At the end he does something really stupid with some money he gets rather than paying back the people who he got put in the hospital or got their homes destroyed because of him...or paying for an immigration attorney for the illegal who has been very nice to him and is at risk of deportation because of his choices. (some friend this guy is!)
At the line level, decently written, but... no.