In September 1926, the Honourable Daisy Dalrymple Fletcher visits Sybil Sutherby, a school friend now living in Derbyshire as the confidential secretary to a novelist. Suspecting that something is seriously amiss, Sybil has asked Daisy to discretely investigate.
Upon arrival, Daisy finds a household of relatives and would-be suitors living off the hospitality of Humphrey Birtwhistle, who had been supporting them through his thrice-yearly, pseudonymous Westerns. When he took ill, though, Sybil took over writing them while he recovered, only to see the sales and advances increase. Now, she fears that someone in the household is poisoning Birtwhistle to keep him ill and keep Sybil writing the better-paying versions.
But before Daisy can even get a decent investigation underway, Humphrey Birtwhistle dies under suspicious circumstances and Daisy must untangle a house full of suspects and a Scotland Yard detective husband who is less than pleased at this turn of events.