Patricia Wentworth 
In the Balance [EPUB ebook] 

The “marvelous” British governess-turned-sleuth helps a new bride who fears her husband intends to murder her (Daily Mail). Former schoolteacher Miss Maud Silver is on her way back to London when, with a violent shudder of the train, a young woman is thrust into her compartment. She’s beautiful, well dressed, newly married, and wealthy—a lethal combination. In a state of shock, Lisle Jerningham explains that she fled her home in a hurry after overhearing a sinister conversation. Her new husband’s first wife died in an apparent accident, and the resultant infusion of cash saved his family home. Now, he’s broke again—and attempting to engineer a second convenient mishap. Miss Silver is unsure whether the drama is real or a figment of Lisle’s imagination—but if this frightened young lady is a target for murder, the killer will have to deal with the governess-turned-sleuth first.  Starring a mature sleuth who “has her place in detective fiction as surely as Lord Peter Wimsey or Hercule Poirot”, In the Balance is a classic British mystery (Manchester Evening News).