London is enveloped by an almost apocalyptic smog that obscures everything, both physically and figuratively speaking. A murderer is wandering the streets, searching for a way to a treasure. Albert Campion is called to help on the case, but he doesn't really do much detective work, appearing instead as a distant character mostly hovering in the background. Misleading, because the series is supposed to contain Albert Campion mysteries. Campion isn't even his real name! Allingham does a lot of dwelling with the characters' personalities and their behaviour and whatnot, but the actual crime solving is left on the sidelines, whereas psychological ponderings take up a lot of space.

I ended up feeling conflicted about the whole book, because Allingham is wonderful at describing London and the effect of the smog. The side characters obsessed with the treasure are bizarre, in a good way. My expectations just didn't click with what I got in the end, and one would have hoped the meditations on philosophical and theological issues had been more integrated into the actual story. Now they seemed disconnected, made reading a bit sticky, and stretched the plot unnecessarily (or more like halted it completely). On the other hand, Campion didn't seem to have a purpose in the story, so he could have been left out entirely without it affecting in any way to anything.

However, despite the poor pacing etc., the gloomy atmosphere and the fascinating ending won me over, so I'll continue with the series. Maybe start from the beginning to see if the novels are any different there, or if Campion is introduced more comprehensively.