This novel is a cross between a film noir and an Escher drawing. It centres around Charles Unwin, a clerk in a huge, extremely hierarchical detective agency. He loves his job and is very good at it. Then one day he is promoted, entirely unexpectedly, to the rank of detective. Confused and out of his depth he has to find the missing Detective Sivart, the man whose case notes he has been typing up for many years.
It has a wonderful cast of characters including the villain Enoch Hoffmann, the femme fatale Cleopatra Greenwood and the thuggish Rook brothers. It is always raining and hats and umbrellas are very important.
It's a convoluted novel. I had to retrace my steps a couple of times just to make sure I'd understood a new plot development, but it's well worth the effort.