There's no specific date suggested for when the action takes place, but the fact that the local hotel has been involved in a couple of seedy divorce cases gives it a 1930's kind of a feel (I've been googling divorce law and London gun shops for this - I really hope I don't end up on some sort of watch list - in 1937 cruelty, desertion, and insanity became grounds for divorce, so the need to prove adultery would not have been so pressing). Service revolvers are a plot feature too, but Wikipedia tells me that they're likely First World War ones.
I've looked all this up because part of the charm of the book is that it sits in the suggestion of a past rather than feeling like it's rooted in it's own contemporary world. A character like amateur sleuth Mr Verity, would always have to belong to an earlier time of larger characters than out own world (whenever it is) makes you feel are quite possible.
Mr Verity is a wonderous creation, a fat man in his 60's, we first meet him carrying a mauve bathing suit heading for the sea. His hobby is collecting antique sculpture (with scant regard for export laws) and being right - the police respect him almost as much as they dislike him.
The woman in the wardrobe is a waitress - Alice Burton. It's an awkward place for her to be found as on the other side of the door, in a room with locked doors and bolted windows, is the dead body of a blackmailer.
The whole book bowls along fueled by a mixture of wit and humour. There's definitely a theatrical edge to it, and the pace is such that you don't really have time to pick faults in the plot. The twist at the end is an absolute peach and very much of a piece with the general underlying humour of the book. It's a fun mystery that resolves itself convincingly enough but the real joy is in Shaffer's descriptions and details - especially on the subject of Mr Verity and Inspector Rambler. This is a tremendously enjoyable addition to the British Library Crime Classics series.