Silent Witness episode 4 recap: how did Nikki and the team identify the hacker and blackmailer?

Episode four picked up straight after the stabbing of Jason Farrell – the barrister who had endured a nasty wound to the chest in last night's cliffhanger. He had managed to crawl himself to safety but – lying unconscious in hospital – he was of little use to the Lyell team. They did, however, uncover his wallet and notice there was a photo missing.

What was it of? Shelley, Jason's fiancé, who told Nikki it was a photo booth snap from the pair's first date. In fact, Shelley had plenty of useful information to dispense, helping Nikki finally get her head around how the trio of deaths in episode three were connected to the massive data breach at Hamilton Ash hospital. You see, Jason had made a decent stab (sorry) of getting clean after years spent addicted to cocaine. He'd fallen off the wagon pretty monumentally but what if he had been blackmailed? He was enrolled on a rehab course at the hospital so the hacker had the evidence to potentially end his legal career.

Meanwhile, we learned more about shifty hospital chief Simon Laing and icy therapist Dr Eleanor Hill: the pair were in a relationship, although viewers saw them exchange nothing but harsh words and a stinging slap delivered by Eleanor.

She was worried about getting caught up in the scandal that was fast enveloping Simon. The hospital's CEO found himself admitting to the board that he had awarded a digital defence contract to an old acquaintance who had paid him for the pleasure – Simon was suspended for his actions and Eleanor was trying to avoid her reputation going to pot, too.

Back at the lab, Clarissa and Max had finally pinned down the identity of hacker "Splinter".

Splinter had been rather stupid, spraying his graffiti tag around and about. Prints were taken from some empty cans at a skate park and traced back to Gary Brockham – a young lad living half a mile from the drop zone where Jason was stabbed. Gary was arrested and brought in for questioning where he admitted to hacking the hospital (he hacks "institutions", you see) but denied any attempt to blackmail. He'd emailed Simon in an attempt to extort money – a message that had, crucially, contained a sample of data to prove he wasn't bluffing. But when he heard nothing back, Gary sold the information on to a contact on the dark web.

Was he responsible for stabbing Simon? It seemed unlikely, especially when Jack located the attacker on CCTV and realised he'd shed his latex gloves in the vicinity. After digging through some bins, he recovered the gloves and a chisel used in the attack. No prints were found on either but the latex gloves narrowed down the list of suspects: most hospitals had fazed them out as common practise but not Hamilton Ash – they were still using old stock. The culprit had access to hospital supplies! But they were also onto the investigation – while examining a hospital glove sample, Nikki was sent a copy of her file (from her recent therapy sessions with Eleanor Hill) and told to ditch the evidence.

Meanwhile, back in his office, Simon – with a bloodied nose thanks to Eleanor – fished around for a key and brushed past his assistant Jane before heading to the basement where he opened a locker and took out a bag of money. He was last seen standing in a stairwell dialling Eleanor – next thing we knew he was lying on the ground, dead, after an attack that saw him fall several storeys to the ground. His hand was still clutching the key.

During his post-mortem, the team found powder in his wound – a substance consistent with rat poison which led Jack and Naomi to the basement where some recent traps had been laid. They matched the key to Simon's locker and found Nikki's hospital file inside.

The confidential notes were now evidence and Jack and Clarissa were forced to examine the harrowing details of her Mexico ordeal – the account she's given to Dr Hill. Realising the full extent of her suffering, Jack – who up till now has been seriously frosty towards his colleague – stood up and gave her a hug.

And in the end it was Nikki's file that pinned the crimes to Simon's PA – Jane. Or should we say Jackie.

Working under an alias, Jackie had one hell of a vendetta against Jason after losing custody of her son in a divorce battle where the barrister had represented her husband. Jackie was a rather unsavoury character whose shortcomings were paraded in front of the entire court thanks to Jason. When Simon was sent Jason's medical records as blackmail, Jackie had seen the message and taken advantage of the information that had fallen into her hands.

Blackmailing Jason, she was determined to take something precious from him – just like he had done to her. So armed with Jason's keys (stolen from his bedside) – and the photo booth picture of Shelley – Jackie headed for his swanky pad, presumably with the intention of killing his poor fiancé.

Luckily, the Lyell team weren't far behind after tracing the prints on Nikki's file to Jackie and setting off in hot pursuit. They got there in the nick of time and apprehended their blackmailer, solving the case.

And in celebration, Jack shared another snog with Naomi. Everyone was a winner.

Silent Witness continues next Monday at 9pm on BBC1