Vigil episode 5 review: Penultimate episode leaves characters in mortal danger

Anyway, what about those reveals? It was clear from last week's events that Jackie was somehow involved in the plot, but it was always unlikely she was the real big bad, and so it proved tonight. It turns out that she had killed Craig Burke, but only so the submarine could surface such that the real villain, Matthew Doward (Lorne MacFadyen), could take his place on the boat. Now, that revelation certainly came out of left field – sure, there had been a few shots of Doward behaving a little suspiciously in the background in previous episodes, but by and large, he's a character who has had very little to do.

This will probably come as a disappointment for some viewers – it's always a bit tastier when the villain is someone we've properly gotten to know over the course of the series, after all – but I thought it worked fairly well dramatically in the context of the episode, especially when Amy finds herself alone with Doward in the very last moments. It also creates some questions as to the reasons for killing Burke in the first place: if the real motive was to get the boat to surface, and not to get rid of a potential whistleblower, then are we to assume that the Russians weren't all that concerned – or at least weren't fully aware – about the information Burke had on their activities? Or did the murder actually serve a dual purpose? Presumably, we'll find out next week.

There was plenty of drama on land tonight as well, with peace camp leader Ben Oakley being unmasked as another Russian asset. I have to say I found this reveal slightly less surprising – there had always been something very fishy about him, especially when he reacted in a rather hostile manner to Kirsten in episode two, but I enjoyed the way he was able to hoodwink MP Patrick Cruden into offering him protection, and it sets up another intriguing chase going into the final episode.

Amy and Kirsten's past relationship was also further delved into, as we (and Kirsten) met Amy's daughter and in-laws, with a couple more flashbacks thrown in for good measure. At the risk of sounding like a broken record, these aspects of the show remain the parts I'm least convinced by – I understand the appeal, and the significance within the story, of giving these characters a past, but I reckon the flashbacks are just far too heavy-handed and detract from the more interesting storylines. Seeing Amy leave her daughter a note before heading into the contaminated part of the boat was fine – and even quite affecting – but I just don't think we needed to have seen all these flashbacks for that to be the case.

Just look at someone like Glover, who has managed to be a complex and nuanced character without the need for any over-egged backstory. There's clearly a past there, we just don't need to be spoon-fed every aspect of it. Anyway, speaking of the coxswain, it looks like his days are very much numbered: it would be some miracle to see him survive his fate at the end of this episode. Despite his rather untrustworthy nature earlier in the series surrounding his hidden relationship with Docherty, I think his actions in this episode make it safe to put him firmly in the good egg camp – a flawed person no doubt, but a fundamentally decent one nonetheless. Anyway, he was a brilliant character and if, as expected, he does bite the dust, it will be a shame to see him go.

Despite a couple of missteps, Vigil has been one of the best new BBC One thrillers for years and as we head into the final instalment we can only hope that it will stick the landing. Either way, it's been a great ride so far.

Vigil concludes on Sunday 26th September at 9pm on BBC One and BBC iPlayer. For more to watch, check out more of our Drama coverage or visit our TV Guide to see what’s on tonight.