At age 28, plain and bookish Lina McLaidlaw lives a life of boredom with her retired parents in an English village.

Her prettier sister has married a rising writer, but Lina never meets any men she could accept until the arrival of charming Johnnie Aysgarth, from an impoverished and disreputable family.

However they are soon married, enjoy a long and expensive honeymoon abroad, and return to a large country house that Johnny has acquired and extravagantly furnished.

Gradually the more level-headed Lina takes charge of the family finances, relying on an allowance from her father, and pushes Johnnie into finding a job.

Later, he cons an old school friend into backing a property development and, taking his gullible partner to Paris, on a visit to a brothel pours so much brandy into him that the man dies.

In this he is aided by Isobel Sedbusk, a writer of crime stories, who often visits their village and enjoys discussing foolproof ways of getting rid of people.

She tells Johnnie that there is a common chemical which is tasteless if mixed in milk, kills instantly, and leaves no trace in the body.

According to William L. De Andrea in Encyclopedia Mysteriosa (1994), this was because the studio, RKO Radio Pictures, was uncomfortable with the idea of having one of Hollywood's leading actors Cary Grant, who played Johnnie, being shown on screen as a devious psychopath.

[1] He wanted an ending similar to the climax of the novel, but the studio, more concerned with Cary Grant's "heroic" image, insisted that it be changed.