The Clock Strikes Twelve by Patricia Wentworth
New Year's Eve, 1940, is unusual for the Paradine family. Departing from tradition, James Paradine makes a speech that changes the course of many lives. Valuable documents have disappeared. A member of the family has taken them. The culprit has until midnight to confess and return the papers.
A few minutes after twelve James Paradine is dead.
It is left to Miss Silver to disentangle the threads that bind the Paradine family in a strange web of dislike, hatred and fear.