In this novel, which continues the Zelda arc (the Eastern European woman first introduced in the last volume), Banks continues to grapple with both the evil that outsiders can do, and the evil aroused in white Britain when xenophobia gets a grip on them.
The main case is the murder of a 12- or 13-year-old boy from Syria, a refugee sent ahead of his family, who gets caught up in the world of drug distribution (the "county lines" - a new phrase for me). That trade, apparently, is being taken over by Albanians with a particularly ruthless line in executions for operatives or allies they deem to be unfaithful, unreliable or disposable. The boy is found stabbed in a garbage bin in one run-down Eastvale estate, but evidence quickly links him to another death, an overdose of an elderly man, in another. This second estate is about to be redeveloped by a greedy English entrepreneur who is hand-in-glove with said Albanians. Living physically as well as economically elevated above the estate, on a hill just above it, is a middle-class largely white district with an active neighbourhood watch, and a recent trauma in the form of the rape of a young woman in the park that joins (or separates) the two neighbourhoods.
Meanwhile, in what seems almost entirely a different book, "Zelda" (her real name is Nelia) is working out her destiny, mostly in London. Making a series of too-stupid-to-live decisions straight out of thriller movies, she pursues the two Croatian brothers responsible for abducting her into sex slavery. After the culmination of that search (I won't spoil it), she goes to Banks (her boyfriend is Annie Cabbot's father, but he's out of the country); there are some stirrings of romantic attraction, but nothing is acted upon, and she certainly doesn't confide everything to him about her actions in London. I'm presuming the resolution of this story will take up a large part of the next Banks novel.
There are a lot of nasty, violent, vicious people in this novel, and because so much of it is spent on the sub-plot I did find that I would have liked more of the cheery Eastvale police department banter as a counteractive.
No spoilers as to the eventual degree of guilt worked out and assigned to the various perpetrators in the two main plot lines. The primary plot is fully resolved. I still get a great deal of pleasure out of these novels, and am not finding them repetitive. Nor do I object, as some reviewers apparently do, to Banks' political thoughts about racism and Brexit - you can hardly avoid it, and I suppose I don't object because his thoughts (those of a "Guardian reader", as one of the neighbourhood watch spits) are, to me, fundamentally right and exactly what you'd hope the police would believe.
Just another step down the path with an old friend.