Millicent McHarg, an eccentric and forthright novelist, is adored by her three granddaughters. When the eldest, Prunella, nicknamed Plumpet, is found hurt and bewildered in her own bed on Christmas morning following a party the night before, her family must at once deal with the emotional pain, and try to solve the mystery. With Plumpet's sisters' help, Millicent prepares to take a grandmother's revenge!