I first read this many years ago, but since I absconded from the cottage with The third deadly sin, I thought I would collect the lot of them. In this one, Edward X Delaney is still married to Barbara, though she spends almost the entire novel in the hospital suffering her last illness. He's also the Captain of the 251st precinct, which is right next door to him. He decides to retire to spend time with his wife while she recovers (which she doesn't, sadly) but is convinced to turn this into an extended leave of absence and further to spend this time running an unofficial investigation at the behest of the Commissioner and a few others. Politics abound behind the scenes. Thankfully Delaney is utterly uninterested in politics, so we manage to avoid most of it.
Again, the narrative is beautifully interwoven between Delaney and the killer, which allows a reader to experience both view points and to appreciate the effect that each is having on the other. There's a fair amount of philosophising, mostly done by Celia Montfort - a woman that is ostensibly the killer's girlfriend, but about whom there is almost no information available at all. Though, to be fair, we know as much about her, her brother and her manservant as the killer does. Delaney also spends a fair bit of time philosophising, but given that his wife's condition is rapidly deteriorating, I'm willing to forgive his dwelling on the meaning of life, etc.
The ending is rather depressing and I'm not sure that it's entirely realistic. I suspect that a serious break with reality is required for it to occur and I thought it well-written and believable, though I do wonder about it's likelihood now that I'm finished reading.