On New Year's Eve, 1942, James Paradine has just discovered the theft of some important blueprints from his office. Calling in Elliot Wray - not only his junior in the firm, but the estranged husband of his adopted niece Phyllida - James orders him to come to dinner that evening. This New Year will ring in not only with espionage, but a confrontation between Elliot, Phyllida, and Phyllida's guardian, James' sister Grace, who runs James' household - as good a recipe for disaster as one could hope for in a month of Sundays.
So why is James acting like the cat who got the canary?
James certainly seems to be taking a malicious pleasure in *something*, but the stolen plans aren't anything to laugh about - and when he makes a formal toast to the family party over dinner, speaking of family loyalty and inviting an unnamed party to confess to something, he really puts a cat among the pigeons: Albert Pearson, distant cousin, perfect secretary, and young to be such a crashing bore; James' solid nephew Frank Ambrose; Frank's wife Irene, fretting herself into premature middle-age over her children (and being helped along by Grace); Frank's bossy sister Brenda, who feels put upon about sharing the running of his house; Irene's flamboyant, cheerful sister Lydia, who takes Irene as a awful warning, and provides a leavening of sense in the Grace-admiration society; cousin Dick Paradine, continually working on getting Lydia to the altar; and Mike, who's hopelessly in love with Lydia, and would rather be in China than at the family dinner. Last, but not least, Phyllida Wray, who left Elliot Wray a year ago only to fall back into the smothering clutches of Grace Paradine.
All in all, not a good group to taunt with an ambiguous accusation and an urge to confession - who knows what might come out. Half the family appears to have visited his study at some point in the evening, and apparently James got more than he bargained for; he's found dead, fallen from the terrace outside his study. Mike, as his heir, falls immediately under suspicion. But Maud Silver, governess-turned-PI, is spending Christmas with her favourite niece nearby - and of all people, the flamboyant Lydia turns out to have met her, and calls her in to tell the truth and shame the devil - no matter what devil turns out to have been the murderer.