But who plays who? Read on for a rundown of the major characters and the actors portraying them...

Stephen Lewis (played by Benedict Cumberbatch)

Stephen Lewis writes children's books for a living and led a happy life with wife Julie and their daughter – that is until three-year-old Kate vanished on a visit to the supermarket with her father. The drama operates on two time frames, looking at Stephen's life two years on from the tragedy, while flashing back to the days and weeks after her disappearance. The loss of their daughter resulted in Stephen and Julie's split but the drama follows the pair as they reconnect and both try to move on with their lives.

Who is Benedict Cumberbatch?

The man needs no introduction. In the past few years Cumberbatch's career has gone from successful to stratospheric, earning an Oscar nomination for his portrayal of Alan Turing in The Imitation Game and going on to play Doctor Strange in last year's smash hit Marvel film. But for many he will always be Sherlock Holmes – his role as Arthur Conan Doyle's detective in the BBC1 series has won him a legion of loyal fans who have followed his career ever since, in projects including 12 Years a Slave, Star Trek Into Darkness, The Hollow Crown and The Hobbit films. Next up, he's putting his cape back on for Thor: Ragnorak and starring in new Sky drama Melrose, also produced by his company SunnyMarch.

Julie Lewis (played by Kelly Macdonald)

Stephen's wife wasn't there at the time of Kate's disappearance. But while he manically searched for their daughter, she retreated into herself and the couple eventually separated with Julie moving to the countryside. The drama picks up with the pair edging back into one another's lives after two years apart – and exploring whether they can move past the devastating loss of their child.

Who is Kelly Macdonald?

Kelly Macdonald has popped up in a host of TV shows and films, on both sides of the pond, including Trainspotting, Gosford Park, Nanny McPhee, Brave and Harry Potter and the Deathly Hallows – Part II. She played Della Smith in the cast of BBC's acclaimed 2003 miniseries State of Play, alongside David Morrissey, John Simm and Bill Nighy, and went on to appear in five seasons of HBO series Boardwalk Empire. Macdonald has plenty of silverware in her cabinet, too, winning an Emmy for 2006's The Girl in the Café, followed by a Screen Actors Guild Award for 2008 film No Country for Old Men.

Charles Darke (played by Stephen Campbell Moore)

Charles is Stephen's best friend and publisher of his children's books. He has established a successful career in politics and is a favourite of the Prime Minister's but, to the surprise of their friends, he and wife Thelma decide to quit London and their jobs to move to the country where Charles reverts to a childhood version of himself.

Who is Stephen Campbell Moore?

You might recognise Stephen Campbell Moore from Alan Bennett's play, The History Boys. Back in 2004, he played history teacher Irwin in the original National Theatre production alongside Dominic Cooper, James Corden and Russell Tovey, going on to portray the character in the 2006 film. He's since appeared in A Good Woman with Scarlett Johansson, Wallis and Edward with Joely Richardson, and 2011 film Season of the Witch where he met his now wife Claire Foy aka Netflix's Queen Elizabeth in The Crown.

Thelma Darke (played by Saskia Reeves)

Thelma is Charles's wife – a quantum physicist who, in the face of his breakdown, moves with him to the countryside and keeps a stiff upper lip around everyone except Stephen.

Who is Saskia Reeves?

The British actress is best known for her roles in 1991 film Close My Eyes, in which she played Natalie alongside Clive Owen and Alan Rickman, and I.D. – a 1995 flick with Reece Dinsdale, Sean Pertwee and Warren Clarke. She also appeared in 2000 miniseries, Frank Herbert's Dune, and co-starred with Idris Elba in series one of Luther.