A young British woman stumbles through the streets of Eckhausen in Germany and collapses. Her name is Alice Webster, and she was abducted from the same town 11 years ago. Her return sends shockwaves through the tight-knit local community, as her family are thrown into turmoil.

As the search for the abductor gathers pace, Alice also appears to hold vital clues to the whereabouts of a second missing girl, Sophie Giroux, whose disappearance was investigated back in 2003 by French detective Julien Baptiste.

Two years on, Alice's parents Sam and Gemma are barely speaking, whilst Alice's brother Matthew has become unhappy and withdrawn. Meanwhile, Julien is in Iraq, following a clue that he believes is key to finding the person who abducted the girls.

After Alice returns to her family home, the Websters struggle to deal with the trauma she has suffered. As Matthew is faced with an unbearable request, Gemma's suspicions about what happened to her daughter begin to grow. The Royal Military Police and the German police agree to share jurisdiction over the case and launch a search for the second missing girl. During a search, Julien discovers a key clue that points the investigation towards a local suspect.

In 2016, war journalist Stefan Andersson is helping Julien make his way to Azwya across an active warzone. What is Julien doing out in Iraq? And will he make it home unscathed? Meanwhile, back in Eckhausen, Gemma and Sam continue to drift apart, while RMP staff sergeant Eve Stone has to deal with her father.

Julien returns to Paris to visit the father of Sophie Giroux, but Remy isn't all that pleased to see him. Meanwhile, Alice is upset by an argument in the house and begs her brother, Matthew, to act against his better judgment in order to help her feel safe. When another unforeseeable trauma hits the Webster family, it looks set to tear them apart for good.

In Iraq, Julien finally comes face to face with the Awol British soldier he has been searching for - but not in the way he expected. The trail of evidence looks like it leads back to Germany, but will Julien and Stefan make it out alive? Back in Eckhausen, Gemma channels her energy into searching for the truth of what happened to her daughter, uncovering a vital clue.

With Sam in hospital, the Websters begin to fracture as he continues to push away his wife and son. Gemma is forced to face up to the devastating truth of the destruction wrought on her family as she makes a statement to the press. While trawling through CCTV footage with German police officer Jorn Lenhart, Julien uncovers a surprising connection that implicates another major suspect.

In 2016, Julien and Stefan return to Erbil to trace the lead they were given and discover a shocking truth that implicates two suspects back in Germany. Gemma continues her determined and desperate search for the truth about her daughter's disappearance, enlisting the help of Eve Stone. Her investigation seems to be hitting a brick wall, before she makes a breakthrough that implies the crimes of Alice and Sophie's abductor stretch further than originally thought. But will she make it to the missing girl in time?

Julien and Jorn's investigation leads them further into the murky underbelly of Eckhausen and the secrets of its conflicting German and British communities. However, as he gets closer to the truth, Julien is dramatically let down by his own body. The Webster family drift further and further apart as Matthew gets involved with unhappy thugs and Sam seeks solace elsewhere.

It is now 2015 and Julien's health is failing, but his determination to track down the missing girl means he has not finished with the Webster case just yet. Back in Germany, the press descend on Eckhausen for a trial when a seemingly vital piece of new evidence comes to light. Gemma is surprised by a phone call from Julien and finds a new purpose that helps break through her stupor. A year later and Julien is still searching for his third suspect when he comes across a name that he recognises. However, he finds himself running out of time as friends in Eckhausen are beginning to question his mental capacity. Can he persuade anyone to listen to him? And will they make it to the missing girl in time? Meanwhile, Matthew's behaviour becomes more and more extreme, culminating in a unhappy altercation with life-changing consequences for the Webster family.

Secrets from the past are uncovered as Julien finally learns the truth behind Alice and Sophie's abduction. But time is running out, and nobody in Eckhausen will listen to him. Has Julien cracked the case, or is he simply deluded? With nowhere left to turn, how far will Julien go in his search to find the truth? Meanwhile, Sam and Gemma are forced to make a heartbreaking choice and are pushed further apart than ever before. As Julien is forced to take matters into his own hands, Gemma joins him in a final desperate race to uncover the truth.

The truth of the events leading up to Alice's return to Eckhausen in 2014 is finally revealed. Meanwhile, in 2016, Sam and Gemma are pulling together and join Julien in a desperate race against time, as they track Alice and Sophie's abductor from Germany all the way to the mountains of Switzerland.