In the 1920's, in post-WWI England, the Honourable Daisy Dalrymple, newly married to Detective Inspector Alec Fletcher, is asked by her brother-in-law to discreetly investigate a series of poisoned pen letters that many of the local villagers have been receiving. When the pompous and unbearable brother of the local vicar is killed by a very large rock dropped on his head from a great height, it seems clear to all that this campaign of gossip has escalated to murder. With the help of her husband, who'd rather she not get involved in murder, Daisy undertakes to uncover the identity of the viper in the local nest is and who that person has driven to murder before the murderer strikes a second time.