SPOILERS: THIS CONTAINS KEY DETAILS FROM THE FINAL EPISODE OF BORN TO KILL

“There are traits that concern me”, observed psychiatrist Helen (Lolita Chakrabarti) of teen killer Sam (Jack Rowan) at the start of tonight’s finale of Born To Kill. No kidding. And tonight the baby-faced psychopath met his reckoning in an extraordinary hour of drama.

Before first, of course, Sam still had some more killing to do following the funeral of his first victim, the poor nurse Cathy.

Having fled to his girlfriend Chrissy’s house and rowed with her gran (who was old and wise enough to have long spotted him as a wrong'un) the elderly woman fell down the stairs.

As she was lying helpless he applied fatal pressure to her carotid artery (on her neck) to finish her off. And then he fled with a distraught Chrissy to meet his staggeringly unpleasant dad Peter (Richard Coyle) who had secured a boat and a plan to flee.

But of course Peter, newly released from prison, wasn’t interested in Sam at all. He wanted Sam as a lure for Jenny (Romola Garai), his first wife and a woman he remained obsessed by. And Chrissy wasn’t too impressed when she witnessed at first hand Sam’s callousness about the death of her gran (she didn’t even realise he’d killed her) and managed to escape him.

In an action-packed final few scenes, Chrissy’s copper dad Bill (Daniel Mays) used his professional training to work out the truth about Sam’s crimes: his daughter was wearing Cathy’s necklace which came from Sam and which he could only have obtained by killing her. A full-scale manhunt was launched as Sam, Jenny and Peter finally came together on the boat.

Peter then attempted to kill Sam, throwing him overboard, leading to Sam’s final moment of clarity: a sudden recall about his dad.

We knew that Peter had killed Sam’s step dad but what the flashback taught us was the savagery of the attack and the genuine love the victim had for the his infant step son. And Peter was prepared to do the same to his son until Sam clambered back on board and smashed his skull in.

“It’s alright. It makes sense now. I’ll be fine,” said Sam in the final moment of dialogue as he was led away by police, leaving poor Jenny alone. If anyone is going to need psychiatric help from now on, it’s her.

What was impressive about tonight’s episode was the way a series which has hitherto been as studiously slow-paced as it has been tense and dark suddenly threw up a flurry of action and excitement.

The wintry, sodium lit urban sprawl provided magnificent atmosphere but the real sparkle came from the fabulous ensemble with Rowan in particular continuing to be adept at capturing Sam’s eerie plausibility.

But we won’t be seeing Sam again. He may have been carted off to prison but co-creator Kate Ashfield assured me that the story has been told in full and there will not be a Born To Kill series 2. Which given the horrors we have witnessed in this impressive drama might just be as well.