Adaptation of the stage play by Hugh Whitemore.

A middle-class homemaker becomes involved in a 1961 espionage investigation in her suburban London backyard. Straightforward yet reserved Barbara, sharing a quiet life with her loving husband and their teen-age daughter, is visited out of the blue by an intelligence agent who cites national security and sets up shop in the couple's bedroom to watch for a "suspicious character" seen in the vicinity. But the agent is really after the family's neighbors, one of whom is Barbara's very dear friend. As the intrigue intensifies, Barbara undergoes a crisis of conscience that tests her loyalties, her confidences, and her sense of ethics.