The Outcast starts with images of idyllic county life. After Gilbert (Greg Wise) returns from the frontline in Africa during World War II it looks like life can begin again for ten-year-old Lewis (Finn Elliot) and his mother, Elizabeth (Hattie Morahan). Then about 20 minutes into the first episode a picnic turns to tragedy.

Lewis never really recovers, the burden of guilt weighing him down. This melancholy little boy is shunned by his school friends and is awkward around his father's new wife Alice (Downton Abbey's Jessica Brown Findlay). He negotiates his way through complex family relations at a time of stiff upper lips and repressed emotions.

Lewis grows into a sullen, despondent young man (now played by George MacKay) adrift in life. He finally finds some level of comfort in alcohol and the jazz dive bars of the 50s, falling for the beguiling Jeanie (Leanne Best). But even here, where it looks like he might find acceptance, he deliberately distances himself from others. He still finds it hard to make connections, and relations with his father grow colder and colder – though he might have found an ally in his home village in young Kit (Jessica Barden) who is dealing with her own growing problems. However, Lewis' actions at the end of episode one will have very serious repercussions.

Sadie Jones adapts her own award-winning, bestselling novel for the BBC and brings real depth to her characters, capturing the sadness lurking beneath the façade of genteel politeness in 1950s Britain. It's a particularly impressive turn from MacKay, reaching deep within himself to portray this self-loathing, near silent loner. With scenes of self-harm and despair, The Outcast is full of raw emotion but its unrelentingly downbeat tone will alienate as many as it captivates.

The Outcast premieres on BBC One, Sun 12 July.