Vigil episode 2 recap: Amy and Prentice clash plus another major death

We'll get to that death later, but first, let's dissect everything that happened on the submarine. The episode opens with the fallout of the system failure seen at the end of episode one, with the crew frantically trying to rectify the situation, and Craig's old bunkmate Gary Walsh injured in the process after being caught in the nitrogen burst. Crucially, Gary isn't the only one feeling under the weather – Adams, who previously suggested he was feeling a little off, claims that his vision keeps blurring and he just doesn't feel right. More on that later.

Anyway, there's certainly no love lost between Amy and Mark Prentice, and several clashes between them form the main narrative thrust of this second episode. Their first encounter comes after Glover tips Amy off about the duty logbook, in which files of disciplinary actions against various crew members are logged. Upon researching, Amy finds that Craig was disciplined far more than anyone else by Prentice, and what's more, there is a disciplinary recorded against Gary Walsh's name, but no reason given. When Amy quizzes Prentice about this he's not particularly helpful (to put it mildly) – instead insisting that the boat's major logistical issues should take priority over Amy's investigation.

Later Amy and Prentice butt heads again, this time when she decides to question Officer Hadlow without Glover being present. During their exchange, Hadlow – who is also reluctant to answer questions – let's slip that "nobody meant to kill him" and "there is a chain of command" but before we can get further clarification on what exactly this means, Prentice has arrived to illegally lock Amy away in an enclosed space. She is forced to stay here while the boat has a close collision with another vessel, and during this incident we learn more about the previous accident we'd seen flashbacks to in episode one: it appears that when her car went underwater, Amy saved her daughter and had to let her (presumed) husband drown. It seems likely we'll continue to learn more about this accident as the series continues.

Anyway, after Amy has been rescued by Glover, she has a third encounter with Prentice – this time arresting him, armed with a theory about his role in Craig's death. She explains that Gary had previously taken heroin to Prentice under the guise that it was Craig's, in a bid to frame him as an act of revenge for what he considered to be his role in his brother's death (the details of which were passed to Amy in a note from Kirsten.) Prentice saw through it, Amy suggests, and disciplined Gary but didn't put the reason in the logbook in a bid to protect him. Later, after their disagreement, Craig and Prentice had a punch up and the head injury inflicted by Prentice led to Craig's death that night. Discovering that he had been responsible, Prentice tried to cover up his role in the death by placing the heroin that he had previously confiscated from Gary at the scene, thus making it look like an overdose.

Prentice initially reacts with scorn to Amy's theory, but it appears to be rubber-stamped when Glover returns with the green fleece and Gary Walsh admits to the heroin incident. At this point, Prentice clearly realises the game is up and admits that Amy is right – and so it seems that, two episodes in, we already have our killer!

Only, it was never going to be that simple, was it? While inspecting the fleece, Amy finds an unusual substance and suddenly recalls Adams' illness, while also remembering the fact that Adams had given Craig mouth to mouth after he was found. And so emerges a new theory: Prentice thought that it was his punch that had caused Craig's death, but there was actually another completely unrelated explanation: he had been poisoned. That explains why Adams has been sick ever since he tried to give Craig mouth to mouth, and also accounts for the bizarre stain on Craig's fleece. The only question is: who poisoned him? It seems clear that however unpleasant he might be, we can probably now rule out Prentice – who genuinely seemed surprised when the poison theory emerged. But then, who could have administered the poison? Everything seems to be priming us for the fact that the conspiracy goes right to the top...

Meanwhile on land, Kirsten is also continuing to prove very useful – and as well as feeding Amy the information about a previous incident that had seen Gary and Officer Hadlow beat up Craig, she also continues her investigation into Craig's activist girlfriend Jade in this episode. Towards the start of the episode, it quickly becomes apparent just how vital the memory stick she found in Craig's room was – with her home being ransacked by burglars as they (unsuccessfully) try to retrieve it. Meantime she tries to get to the bottom of Jade's relationship with Craig and asks her if he was on the submarine to spy for her.

They spend some time at the campsite where Jade lives, and Kirsten tells Jade they reckon Craig was murdered, as well as talking to her about the memory stick – which Jade tries to convince her to hand over. Naturally, Kirsten doesn't oblige and tells Jade to be careful – and to report anything if she feels in danger, but Jade appears to have other ideas. Later, she tells her friend that she has had contact with someone who claims to know something about what happened to Craig – and that she is going to meet him tonight. That doesn't sound like too great an idea, and of course, it all goes a little pear-shaped. Standing on an empty road near the camp waiting to meet her source, Jade gets spooked and calls Kirsten asking for her to come. Sadly, by the time Kirsten arrives someone has already got to Jade – and she is found dead in the water. And so there we have it, another death.

Whatever way you look at it, it's now clear that this conspiracy goes a lot deeper than it first appeared – and is certainly more complex than Amy's original theory about Prentice killing Martin with a blow to the head. The fact that there is poison involved, and that there have now been deaths both at sea and on land, suggests that this is rather a grand plot, while it is also plainly evident that there is some kind of cover-up going on. Throw in the fact that no one seems to know why the submarine's reactor suddenly stopped, and the very real possibility that there is an enemy boat on their trail, it's fair to say that things are not quite plain-sailing aboard Vigil.

The one silver lining is that before Jade was killed she was able to send the password for the protected files on Craig's memory stick to Kirsten – it seems likely that whatever is said in those extra clips will come in very handy for the investigation. We've got just under a week until we find out.

Want more Vigil content? Find out who sings the Vigil theme song or discover where Vigil is filmed with our location guide.

Vigil continues on BBC One on Sunday 5th September at 9pm. If you’re looking for more to watch, check out our TV Guide or visit our Drama hub for the latest news.