Silent Witness episode 4 recap and review: Stolen identities and jealous exes

You see, the couple raising the kids as their own were not actually the parents at all, but their old friends the Garricks – who had killed the real Trask parents and taken over their life and their children. Laura had been killed because she knew Tim Garrick from school and had spotted that he was committing identity fraud – so she was murdered before she could report the incident.

Now, this does beg the question as to how literally nobody else had spotted that the Trask parents had suddenly completely changed (they really don't look all that similar to the Garricks), or for that matter how the Garricks had supposedly vanished off the face of the Earth without being reported as missing persons. Neither couple can have had that many good friends. When coupled with the Trask childrens' stunning lack of protest or unrest as their supposed mother left them in the car to go and drown herself on the beach, this probably goes down as one of the more implausible Silent Witness endings in recent years.

Anyway, after two episodes of new Lyell recruit Adam seeming to be able to do anything, it was nice to see him have a moment of vulnerability as he revealed one thing he can't do: swim. This led to Jack saving the day by plunging into the freezing depths and saving Sally before she drowned – the first of many times that he'll be forced to do battle with water this season, according to David Caves. Perhaps that incident will lead to more of an understanding between Jack and Adam in future episodes because the former had been behaving a little petulantly throughout this doubleheader.

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Meanwhile, smarmy ex-copper Ron Radford (Patrick Baladi) wasn't off the hook completely – he might not have killed Laura, but he's still set to spend some time behind bars for his attack on bus driver and secret sperm bank owner Frank Johnson (Jack Deam), who he coincidentally attacked in exactly the same manner as Laura had been killed. It appears that he was nothing more than a jealous ex – he'd set his sights on Frank when he discovered it was him who had got Laura pregnant, and was determined, it seems, to seek revenge.

Anyway, we also saw another instalment of what David Caves has jokingly termed "Keeping Up With The Hodgsons" as the family drama from the first part of the doubleheader continued into this concluding part. Ryan was furious with Jack when he discovered that Cara had been told he was in jail, but by the end of the episode, the quarrel seemed to have been resolved, with Cara visiting him in prison. Only the drama certainly won't end there: the final moments of the episode saw Jack putting a swab in his mouth, as he prepares to take a DNA test to determine if he might actually be Cara's father. Now that could lead to an awkward conversation...

Meanwhile, Jack and Nikki for the most part seem to be enjoying each other's company at the moment – living up to the pre-season tease that they would find themselves becoming increasingly close to one another over the course of the series. There's plenty of banter between them that almost feels a little like flirting, while there was an interesting conversation about what they thought about 'the whole kids thing'. "I remember joking with Harry once that I would end up a dried old prune," Nikki tells him. "10 years later it's not so funny." It will be interesting to see how this develops over the remaining six episodes.

Silent Witness continues on BBC One on Monday 20th September at 9pm. Check out what else is on with our TV Guide, or visit our Drama hub for all the latest news and features.