The veteran detectives find themselves faced with a series of obscurely linked murders taking place at 4am, apparently the time when people are at their lowest ebb to the extent that generally even murderers steer clear of it. They were retconned a few books back not to be quite so ancient as in the series' earliest entries, but nonetheless death and decline dog their steps even beyond the killer's victims. A killer to whom the readers are introduced fairly early on, meaning the interest is less whodunnit than why, and how many of his targets will make it out alive. Eccentric old Bryant and ladykiller May aren't rubbing along nearly so well as usual, something with which working nights definitely doesn't help, and there are other tensions simmering in the Peculiar Crimes Unit too – though I'm not convinced this is quite such a new problem as the book sometimes tries to suggest. Equally, Bryant seems quietly to have lost the recently acquired condition whereby he would come unmoored in time and be able to consult great Londoners of the past – a shame, as I've always enjoyed the series most when it veers strangest. But on the other hand, my usual bugbear, the perennial subplot about threats to shut down the Unit, feels a lot less forced in our chill new era of savage cuts to police funding. Yes, there are still trying moments, not least when Bryant and his oddball contacts get into speechifying about those young people with their devices and how nobody talks to their neighbours anymore, and the story's action and unattributed narration seems to support them. But the resolution flips that right around, showing the damage the old ways could and can still do, and the descriptions of London are often scalpel-sharp, right down to little details like the greasy spoon where "Across the window were laminated aerial shots of breakfasts, photographed like studies of skin diseases". And even more so than usual, this one seems woven around with locations I know either regularly (Whitechapel, Leadenhall, the Black Friar) or have recently passed through for the first time in a long while (the Unit's home territory of the Cally Road, but also Hampstead station). I too recently went on a batwatching expedition that didn't go to plan, though in my case it was just noisy kids rather than a murder; I too have been bogged down in the new Philip Pullman. It's all left me with a yen to visit cover-star sundered boozer the Ship & Shovell, especially after that cliffhanger.