Nothing Venture — Patricia Wentworth

A plucky young bride risks it all to save her thick-headed husband from a nefarious plot against his life in this classic British cozy mystery.
 
Jervis Weare is in a predicament. According to Ambrose Weare's will, his grandson must marry within three months or the vast estate goes to his great-niece: Jervis's fiancée Rosamund Carew. But the deceiving society beauty has just dumped Jervis, which leaves him scrambling to find another bride.
 
Nan Forsyth has secretly loved Jervis for ten years. He has no inkling that Nan once saved his life and is now about to come to his rescue again. She knows that with her working-class background and the emotionally fragile sister she's raising on her own, she's hardly the proper wife for Jervis. Yet marry him she does; though to Jervis, it's strictly a business arrangement. They're barely wed before the past comes back to haunt them -- a past Jervis can't remember, but someone else does. Now Nan must save Jervis one last time before a murderous plot a decade in the making comes full circle.
 
Nothing Venture is a classic British mystery from the acclaimed author of the Miss Silver Mysteries.