It's 1923 and in a decade that promises excitement and liberation, Pearl Glenham and her father are invited to a mysterious country house party on the Dorset coast, by a total stranger. Her father claims not to have any prior association with Highcliffe House, but upon arrival, it is apparent that he has a shared history with several of the guests, although he won't admit it. Belatedly discovering that her father was blackmailed into attending, Pearl's worries are compounded when their host fails to arrive. . . Intimidated by everyone at the party, she escapes to the nearby cove and stumbles upon a mysterious mercury clock hidden in a cave. This strange encounter sets in motion a series of events that will culminate in an horrific house fire, claiming the lives of all the guests, including Pearl herself. But then Pearl wakes up back in the cave, seemingly destined never to live past midnight. She can repeat the day. But can she change its outcome?