But if you were left a little confused by the Soho private eye’s conclusions, never fear – because we’ve laid out the most important points for you to get your head around.

Why did John kill Lula?

After finding out that Lula (Elarica Johnson) had tracked down her biological half-brother Jonah Agyeman (Abubakar Salim), adoptive brother John (Leo Bill) became furious, feeling that Lula was betraying the family created by their adoptive mother Lady Bristow while also feeling inferior compared to his more loved and successful sibling.

This led him to resolve to kill Lula, just as he murdered his popular brother Charlie when the pair were children.

Who was Charlie, and why did he matter?

Charlie Bristow was the brother of John and the son of Lord and Lady Bristow, as well as a childhood friend of Strike’s (giving the detective a connection to the family). The young Charlie died tragically when he rode his bike into a quarry, but his uncle Tony Landry (Martin Shaw) always suspected that an envious John had something to do with the death, as was seemingly later confirmed by Strike when he found Charlie’s bike bell in John’s car.

This incident led Tony to advise against the Bristows adopting Lula in the first place, out of fear for her safety – but when he hinted at his reasoning to the late Lord Bristow, it caused a rift between them.

Why was the will important?

The new will Lula made (revealed to John after he gained re-entry to her flat again later on) would give all her money to Jonah, cutting the Bristow family out entirely. In the episode, Strike (Tom Burke) theorises this is what pushed John into killing her on that night in particular, before the will became known to others.

If he killed her that night she’d die intestate, meaning her mother Lady Bristow would inherit everything. Given Lady Bristow’s own ill-health, in practical terms this would means the money would soon be John’s – though Strike speculated that money was only a secondary motive to John’s jealousy.

Throughout the three episodes John had been looking for the will, not realising that it was hidden beneath the false bottom of Lula’s old handbag.

How did John kill Lula?

Departing Lula’s flat after an argument, John decided not to leave her building, instead ducking into the vacant flat on the floor below that was being set up for visiting rapper Deeby Macc. Hiding there he found a black hoody and leather gloves dropped off by fashion designer Guy Somé for Macc, which he wore as a disguise along with some flowers he took from the room.

Coincidentally, the hoodie was similar to one worn by Lula’s brother Jonah as he waited outside trying to drum up the courage to go in and see his half-sister – this meant that John and Jonah were initially mistaken for the same person caught on CCTV.

In the flat, John followed Lula out to her balcony and threw her from it before departing, his exit masked by the coincidence of doorman Derrick (Brian Bovell) taking a quick swim, leaving his desk unmanned for half an hour.

Why were the flowers so significant?

John took the bouquet of flowers from the Deeby Macc flat (sent to the rapper by film producer Freddie Bestigui) to cover his face when Lula answered the door, making her more likely to let him in.

Afterwards, the flowers became a key piece of evidence as Lula had not ordered or been sent a bouquet, meaning that they had to have come from within the building itself and suggesting that her killer had struck from inside the complex.

Who killed Rochelle?

John murdered Rochelle Onifade, Lula’s friend who lived in a shelter, because she knew about the new will (which named Jonah as the sole benefactor). Rochelle successfully extorted money out of John to keep the news quiet for a while, but eventually he decided to kill her after it became clear Strike was trying to get information from her.

Why was Tansy Bestigui out on the balcony?

Tansy Bestigui (Tara Fitzgerald), a resident on a lower floor of Lula’s building, heard the shouts of Lula and John’s argument as she stood out in the cold of her own balcony. She had been forced out into the snow in her nightie by her abusive husband Freddie, who disapproved of her cocaine habit and aimed to punish her – but instead the treatment led her to overhear the beginning of Lula’s murder and witness her fall to the ground.

Initially, she told doorman Derrick Wilson (Brian Bovell) about what she’d heard, but later changed her story to hide the truth of her husband’s cruelty.

Why did Tony’s false alibi confirm John’s guilt?

During the course of his enquiries Strike discovered that Tansy was having an affair with Lula and John’s uncle Tony, and that his alibi – spending the evening of Lula’s death with Lady Bristow – was in fact false.

Initially this caused suspicion to fall on Tony, but when Strike realised Tony was still far away from Lula’s building on the night in question he realised that John’s shared alibi (he said he was with Tony at his mother’s house) was similarly bogus.

What evidence convinced the police?

The combination of evidence that damned John included directions placed in his satnav to his victim Rochelle’s house (after claiming he’d never heard of her) and DNA evidence transferred by the leather gloves he wore to kill Lula, after he sweated his way through the porous material.

The existence of the will, Tansy’s testimony and John’s physical attack on Strike also presumably played some factor in his arrest, though this wasn’t seen onscreen.

And finally....why on earth did John hire Strike in the first place?

Given his own guilt in the matter, viewers might be left wondering why John hired Strike to investigate the closed case in the first place, with the subsequent enquiry opening the can of worms that eventually led to his own arrest.

But while it's not entirely clear in the finished drama, in Rowling's original novel Strike's hiring is presented as John's attempt to frame Jonah for Lula's murder. This was a precaution due to the fact that John knew Lula had changed her will in favour of Jonah - if the will ever resurfaced, her half-brother would inherit millions, but if he'd been convicted of her death the money would automatically revert to the family, and subsequently John.

This is referenced in John and Strike's final confrontation in the TV adaptation, when John references the discovery of Jonah Agyemen as "quite an achievement" and considers it the end of Strike's involvement in the case.