“This is a true story. What follows is based on extensive research, interviews and published accounts, with some scenes created for dramatic purposes,” a card on The Sixth Commandment advises.

The four part UK drama centres around the Maids Moreton Murders, a case that gripped the UK in 2015.

Written by Sarah Phelps (A Very British Scandal, The Pale Horse) and directed by Saul Dibb (The Salisbury Poisonings) it is an eerily fascinating anatomy of murder by the hand of Ben Field (Éanna Hardwicke), a strapping, charismatic young man who mesmerised wealthy lonely Brits into bequeathing him their estates.

Call him a paramour, Casanova, gold-digger or parasite, he was everything retired English teacher Peter Farquhar (Timothy Spall) unwittingly desired when their paths crossed during one innocent lecture.

Deeply-religious Peter was also a closeted gay man who had never been loved.

“I do not think it is possible for me to be loved, in that way,” he tells a sympathetic friend and vicar.

But when Ben appears to be enamoured by his love of literature, Peter forges a friendship which fasttracks into attraction at a rapid pace. There’s a quickie commitment ceremony of sorts before Ben moves in, much to the horror of Peter’s concerned brother Ian (Adrian Rawlins).

“I have to be untouched, unloved, and live only a fraction of my life?” asks Peter.

But Ben, aided by a sheepish student friend Martyn (Conor MacNeill), is manoeuvering behind the scenes, including with designs on Peter’s assets.

By episode two Ben has set his sights on one of Peter’s neighbours and spinsters, Ann (Anne Reid) who also falls under his spell. But niece Anne-Marie (Annabel Scholey) has her suspicions about the increasing intimacy and obvious age gap.

The Sixth Commandment explores issues of trust, vulnerability and quietly crushes any fairytale dreams of being swept off our feet by the elixir of youth.

It’s also a masterclass of acting from Timothy Spall, in particular, as the fragile, conservative teacher, trapped for decades by his own feelings of shame and conflict of sexuality and faith. It’s hard not to be moved by his blind folly in placing so much trust in a young man whose drive was entirely materialistic.

Anne Reid is equally sublime in her performance of the gentle Ann, whose world of tea and scones and quiet retirement is thrown asunder by the affections of a much younger man.

But the series would be nothing without Éanna Hardwicke in a gift of a role as the duplicitous Ben. Hardwicke never overplays his part, always leaving Ben’s victims wanting more.

The other fascinating relationship is with student Martyn, whom we only glimpse as being subservient to Ben in blink-and-you’ll-miss-it exchanges. I can’t wait to see how this is explained in later episodes.

Tragically, you never get the feeling you are watching a work of fiction here. With its engrossing script, commanding direction and brilliant ensemble, The Sixth Commandment never puts a foot wrong.

If in doubt, the series is sadly dedicated to the memories of Peter Farquhar and Ann Moore-Martin.

Don’t miss it.

The Sixth Commandment premieres 8.30pm August 24 on BBC First.