In 1968, Charlotte Vance was one of the few women employed by the National Security Agency in Washington, D.C. She put in long hours and was working when a fire started in her home. Her daughters and husband were killed. For 50 years, she has felt responsible for their deaths. In 2018, when a former colleague from the NSA mentions a top secret government agency that is experimenting with time travel, she decides to apply.

After a devastating storm kills her family, Harper Close is suddenly whisked away to an alternate reality in which they're still alive—but don't remember her. With the rare chance to change fate, can Harper prevent a tragedy? With time slipping away, Harper faces a daunting task: to convince her family and the skeptical townsfolk of the need to prepare for the impending disaster, even while evading a menacing figure from the town's mysterious past, who is determined to kill her.

Determined to save the antiques store she has inherited from ruin after the unexplained disappearance of her parents, Sarah Lester discovers a jumbled collection of vintage postcards that leads her on a journey through time. Unprepared for the story the postcards weave about their reclusive former owner, Sarah’s life is thrown into disarray as she is transported to Victorian London, colonial New Zealand, and to the British Raj in 19th-century India.

May 20, 2019: Homicide detective Mallory is in Edinburgh to be with her dying grandmother. While out on a jog one evening, Mallory hears a woman in distress. She’s drawn to an alley, where she is attacked and loses consciousness. May 20, 1869: Housemaid Catriona Thomson had been enjoying a half-day off, only to be discovered that night in a lane, where she’d been strangled and left for dead. When Mallory wakes up in Catriona's body in 1869, she must put aside her shock and adjust quickly to the reality.

On a serene night in 1953, Sally Mason, a dedicated wife and mother of two, drives a twisting road on her way home from night school. Suddenly, a mysterious bluish-white light descends over the road. Terrified, Sally slams on the brakes. After a flash of bright light nearly blinds her, she passes out, awakening to the persistent knock of a police officer on her car window. When she sees the officer and remembers her frightening experience, she screams and faints, and is rushed to the hospital.