On her way to visit her grandfather Vic at a retirement home, an attractive mother named Leanne disappears while buying flowers from a van parked off a highway, leaving her young son and daughter alone. By the time police have been notified, the two children have also disappeared, triggering a desperate search led by Detective Iain Barclay and his sergeant, Amy Foster. As night falls, Leanne's husband Matt waits at home for news with his teenage stepdaughter Tanya, while Leanne's parents, John and Barbara, struggle to come to terms with the day's shocking events. The next day, Matt awakens to news of a discovery from a stranger named Sarah Wheeler, as well as a lead to a loner named Kyle Betts, whose mother Hazel works at the home where Vic lives.

Barclay and his team pursue their leads in the case as press officer Defne 'Tops' Topcu organizes a press conference. Convinced by Sarah to attend, Matt learns his missing wife is pregnant--news that shocks both him and Leanne's parents, Barbara and John. Meanwhile, Hazel suspects her son Kyle may have been involved in the abduction, and makes a call to the police. Another major breakthrough occurs when the flower seller is located, and when a young reporter named Josh Fairley gets Vic to give him the key to a trailer he owns.

In the wake of a 28-day police review, Barclay has turned Leanne's disappearance into a murder investigation--and Kyle Betts is the prime suspect. Day 28 is also Matt's birthday, and he spends it mostly in the company of Sarah, much to Leanne's parents' chagrin. Monitored by liaison officer Simone Farnes and increasingly isolated due the suspicions raised against him, Matt is monitored by a marine buddy named Gary, who has agreed to be an informant. Matt and Farnes also make a disquieting discovery: a matter of days before Leanne disappeared, she bought a one-way flight to France, where her ex-husband, Daf Parry, now lives. Could Leanne have planned to go missing after all? As these questions surface, so does a body, raising fresh fears for Leanne's family.

As the investigation drags on, Matt finds himself in a riff with Leanne's parents after he gives an interview at home with a TV crew. Later, as Tanya accompanies her father to the mall, hoping to travel with him to Paris, Matt and Sarah spend the afternoon at a local fair and road race in a park, which ends with a grisly discovery that takes the family on yet another emotional ride.

The discovery of a burnt-out van offers fresh evidence to Barclay's team, but the prime suspect slips away at a most inopportune time. As a furious Matt joins Gary (and the police) in a nighttime stakeout at the home of Hazel Betts, Amy celebrates her retirement with farewell party at a pub that ends up embarrassing its guest of honor. But Amy's work on the case isn't quite finished--several new clues bring her and Barclay to the verge of finally solving the case.

When a train is delayed by an apparent suicide, PC Laurie Franklin is called upon to help. Later, she connects the case to the abandonment of a baby on the same day.