This is the fifth book in David Robert's series about the detective couple Lord Edward Corinth, with all his establishment connections, and independent minded, communist journalist Verity Browne (any resemblance to another prewar sleuth couple can't be entirely coincidental). Set in the 30's they aim to recreate the style of the golden age detective stories, though with a consciousness of history - war is known to be getting closer (this story is set in 1937 - Browne spends much of the time reporting on the Spanish Civil War, allowing a scene in Guernica) - than could be the case with stories written at the time.
At the beginning of the story Corinth is asked to investigate leaks from the Foreign Office - Churchill is getting sensitive information from somewhere and is using it to fuel his campaign for British rearmament. Corinth agrees to do what he can, however, having met the great man he finds himself in sympathy with his views and unhappy with trying to thwart him. Fortunately a body soon turns up so he is able to redirect his energies to finding the murderer.
Thereafter, the story ambles amiably along and in due course justice is done.
I enjoyed it and it's perfectly readable, but the detective story element does gets rather lost in other strands e.g. a) the continuing transformations of the main characters - Verity's main role in the story is to provide Edward with sufficient emotional upheaval to cause him to question his instinctive political/ social loyalties, whilst his pragmatism is used to mildly temper her idealism. And b) there is a sense that some of the political/ espionage elements are being flagged up so that they can come to a head further on in the series - fine but it feels as though these elements of the plot and some reappearing characters are only there so they can appear more substantial several books hence.