Two "Golden Age" Mysteries

Ngaio Marsh, The Nursing Home Murder
Originally published 1935
Available as an ebook.

On the eve of the introduction of a bill in Parliament that will give the government expanded powers to crack down on fringe political groups, the Home Secretary (chief supporter of the bil), Derek O'Callaghan, is taken to a private hospital and operated on (he has a burst appendix).  And he dies.  It is subsequently discovered to be hyoscine poisoning.  Suspicion falls on a fairly large group of suspects.  One of the doctors--the anesthesiologist--is a eugenicist.  After much back-and-forth, Alleyn discovers both who committed the murder and how it was done.  Alleyn is still way too unprofessional for a professional.  The politics of the book are distressing, frankly.  And, as a whole, it's an example of the sort of murder mystery that inspired Raymond Chandler's line "Hammett took murder out of the Venetian vase and dropped it into the alley...Hammett gave murder back to the kind of people that commit it for reasons, not just to provide a corpse; and with the means at hand, not with hand-wrought dueling pistols, curare, and tropical fish. He put these people down on paper as they are, and he made them talk and think in the language they customarily used for these purposes." 

Patricia Wentworth, Grey Mask Originally published 1929
Available as an ebook.

Highly implausible, but entertaining.  Maude Silver is a private detective in London.  Charles Moray has returned to England after 4 years wandering around the world in search of adventure.  He overhears, in his family homw (which has been uninhabited), what appears to be a plot to kill someone.  He also sees a woman who appearst to be involved and who was his fiance (she called it all off, and he left the country), Margaret,  Moray eventually hires Miss Silver, but resolutely withholds information from her.  After much intrigue and adventure, we reach the resolution and everyone will apparently life happily ever after.  There is much that is wrong with this book.  Miss Silver has almost no personality, and, until the final scene, is seen only in her office.  (Which is to say, she does not appear actively in the narrative.)  All the characters do relatively stupid things--failing to keep their presumed friends and co-investigators involved.  The principal villain, instead of killing our hero and heroine, simply locks them in a hidden cellar in his basement and departs to the continent.  (He is providentially killed in an airplane crash--which apparently kills a number of quite innocent people as well.)  The notion of a 20-year long, successfully-run theft and blackmail racket (including people who change their names and manage to be taken on in the homes of wealth folks, with Scotland Yard, um, somewhat unobservant) is implausible.  But it reads well.  (Chandler’s critique, above, applies here as well.)