Warning: Major spoilers ahead

At the inn, Bull continues his investigation by talking to local conspiracy theorist Osian, who believes children will “condemn humanity to a hellish future”. Asking about the incident with Cefin at the playground, he maintains that he was at the inn all day, something his sister Carys backs up.

Carys notes that there’s fear in town that someone within the community killed Cefin, prompting Bull to ask if she thinks someone is capable of such a thing. She tells him anyone is, under the right circumstances.

The next morning, Jackie is pondering over the strangely similar, astronaut-like drawings made by Cefin and Nessa before both of their disappearances. She then makes her way to the Rees family home to check in on James, Cefin’s best friend who has been greatly troubled and not sleeping since his death. James’s mother, Cara, welcomes her in.

After the police temporarily set up base at the local ice-cream shop, D.C. Jess Deng updates the officers on the case so far – Cefin was last seen after school with James; James returned home at 5.30pm; Cefin’s body was found at 7.30pm, missing his blue wellington boots. While he was found in sea water, fresh water was found in his lungs, so the body must have been drowned elsewhere and then moved.

Frustrated at how slow Deng is going, Bull takes over the briefing, explaining fresh water can be found “anywhere with a hose”. When Deng suggests Cefin’s death could be linked to the disappearance of Nessa Taman, he strictly tells her that they’ll only link the deaths when they find a link between them.

As the team are sent to work, Bull tells Deng to interview James Rees, while he focuses on finding out more about the pipeline leading to the ditch Cefin was found in.

At James’s house, Dylan and Jackie keep him company as he watches TV. Jackie shows him the picture Cefin drew, and he says it’s “the Bee Man”, before commenting that the nasty sting on his hand is nearly healed.

When Jackie asks if the Bee Man has a name, he says it’s Kieran – which Jackie recognises as Kieran Benbow. James shares that Kieran had bought Cefin a present for his birthday, but when Jackie asks if they were with Kieran after school the day Cefin died, they’re stopped by Cara, who chastises her for grilling her son and pulls him away.

Jackie asks Dylan why the boys would know Kieran, and notes he was once a suspect in Nessa’s disappearance. She asks if it had never occurred to him that what happened with Cefin might be connected to Nessa before leaving to talk to Kieran herself.

Bull heads out onto the marshes with environmentalist Gareth Morgan, who notes the pipeline must be privately owned as it’s not council owned. Perhaps it could be connected to the houses on Spider Island, just beyond the marsh? Gareth comments that with the high tides, they must have put it in over the past fortnight, which makes Bull question how the storm is set to affect them. Unfortunately, he doesn’t know.

Gareth then apologises for ‘putting Bull on the spot’ the day before by recognising him. He didn’t mean to make him uncomfortable, especially as he’s in town in a professional capacity, but it was nice to see him again. Bull awkwardly makes his excuses and leaves, leaving a tension between them.

Jackie heads to see Kieran Benbow at his home on Spider Island via a ferry driven by teenager Cathy. Kieran lives on a boathouse on the island, home to a small community that lives off the land. Though he has been living as a recluse these past years, he tends to beehives he keeps nearby.

When Jackie knocks and he doesn’t answer, she lets herself into his house. From there, she sees him returning, and he’s not alone... On the approach to the houseboat she notices nim having an argument with Shell Hill. Panicking at being discovered in his home univited, she hides in one of the backrooms, but she is soon caught. But not by Kieran – she’s found by Bull, who is also following a lead that brought him there. He threatens to arrest her for breaking and entering and warns her to back off, before distracting Kieran long enough for Jackie to make her escape. On her way out, she notices that Kieran owns a child-size beekeeper outfit.

Back in town, Jackie heads to the local butchers, run by Shell and Danny Hill, with the intention of questioning Shell. Danny is behind the counter, and he says that she’s at the family farm but he couldn’t face it. He confidentially tells her that the police have informed him that someone moved Cefin’s body. Deciding not to open the shop, he tries to give her meat that will go rotten otherwise (even though she’s vegetarian) before having a panic attack in front of her, breaking down.

He makes her promise that she’ll share anything she finds out, and she decides to share that they’re talking to Kieran Benbow. Danny is confused why Kieran would be questioned and she pushes it, telling him that he was seen in the woods on the day Nessa went missing, and she’d heard he’d been spending time with Cefin, even giving him a present. Danny’s upset turns to anger and frustration, wanting to know more, and she apologises for telling him anything and leaves.

Enquiries continue, with Deng talking to James, and Bull talking to Kieran. As they pass each other at the police base, James and Kieran deliberately avoid each other’s gaze as they walk between interviews.

Interviews are being conducted in the ice-cream shop’s kitchen and videotaped on a camcorder. Bull asks Kieran why he moved from a bungalow on the seafront to a place on Spider Island, he says the council bought it and knocked it down about a year ago. Nervous and shifty, Kieran celebrates his small community as environmentally conscious, which prompts Bull to ask how that works considering they’re pumping seawater downhill into Morfa Halen, which is already half underwater.

Kieran turns on Bull, saying their interview three years ago over Nessa’s disappearance has stuck with him ever since, meaning people avoid him and treat him with suspicion. Bull tells him that, considering Cefin was found with a bee sting on his neck, in a ditch he drains water into, he needs to start answering questions.

Kieran confirms he knows Cefin but denies being with the boy on the night he died. He then demands a lawyer, saying he only agreed to talk about the pipeline. Switching tac, Bull instead talks about drain. Kieran says it's to save the houses from going underwater, and hands Bull a list of everyone who knows about it.

Bull hands the list to Deng, saying she needs to interview them all, and she shares that James refused to speak to her - not even saying his name. She’s tried to find more links between Cefin and Nessa, noting there’s crossover between people that have been interviewed. A Romanian farmhand, August, came in for an interview for Nessa back then, only to not provide a statement as they were unable to find an interpreter before he changed his mind.

Bull notes that there was nothing to suggest a connection, especially in this tight community. Deng mentions the contruction manager Mac Jones has refused to hand over a list of labourers working on the sea wall until he speaks directly to Bull, though she doesn’t know why.

Jackie continues her own investigation, ducking under police tape to revisit the ditch where she found Cefin. Bull catches her and demands to know what she’s doing. Jackie tells him about the child-size beekeeper outfit she saw on Kieran’s boat, and tells him to bring it in. Bull’s furious she’s pushing herself into the investigation, but she says she can’t help it as she’s part of it, showing the pictures Nessa and Cefin drew before they went missing.

He demands she stop playing detective, saying she’s too close to the investigation and too impulsive to think clearly. He warns her she’ll be arrested if she continues to interfere, but she insists that the two cases are linked and he needs to start seeing it as such.

That evening, Bull heads back to the hotel where he finds Deng grabbing a bite to eat. Joining her, he admits defeat, giving her a chance to plead her case that the two cases are connected. She tells him she knows why he doesn’t want the two cases to be linked: because it would mean his previous accusation against Lydia Taman – Nessa’s mother and Jackie’s sister – was wrong. She asks if that’s why Jackie resigned, and he brusquely tells her Jackie was fired for gross misconduct, before leaving abruptly.

That night, the town settles down. The pub fills out with locals for the night; Bull conducts some research on mushrooms in his room; Jackie visits Dylan; Kieran returns to the Spider Island community, whittling by a campfire; young James struggles to sleep. At the Hill house, Danny and Shell have an argument, resulting in Danny storming out with a duvet to spend the night elsewhere.

The next morning, while lying in bed with Dylan, Jackie dreams of playing with Nessa on a swing, before stopping off at Shell and Danny’s on the way home, spotting flowers outside their door. Shell is in no mood to see her though, furious that she had told Danny about Kieran seeing Cefin, prompting him to spend the night away from her for the first time in 16 years.

Jackie tells her she saw Shell at Spider Island with Kieran, and Shell scolds her for being nosy and sticking her oar in where it doesn’t belong. She insists that Kieran is not involved “in the way she thinks”, prompting Jackie to push her further, noting that she had been seeing Kieran at some point… around the time Cefin was born. Shell is stunned to silence but eventually tells her to stay out of it and goes back inside.

On the Bevan farm, Danny is met by Eddie Bevan, Shell’s brother, who angrily demands he head home and be with his sister. Bull heads back across the causeway to speak to pathologist Irene Hassan, who confirms Cefin was killed. She also notes the hair found on his body belongs to an unknown person, but no other trace DNA indicates someone wore protective gear.

She concludes bruising on the back of his neck were finger marks from someone holding him underwater, with the water containing lye, which had burned Cefin’s eyes.

After his meeting with Irene, Bull heads to the sea wall construction site to speak to Mac Jones and pick up the list of the construction team who were working that night.

At the yard, Mac points out Dylan, stating he was working at the offices alone, not directly on-site, the night of the murder and before Cefin was found. Mac shares Dylan has a criminal record from when he was younger, but says he is a “good guy” and didn’t want that going against him “knowing what police are like”. Mac also shares his hopes of reopening the amusement park the yard is currently based on, even with the town under threat, saying Morfa is “home”.

On the beach, the local neighbourhood comes out in force for a memorial vigil in honour of Cefin, getting the attention of Bull and Deng in the process.

The memorial is led by Solomon, who eulogises his grandson and says that the town was “everything Cefin knew and loved” and they must all stick together for what’s to come. Solomon then announces that the police believe his death wasn’t an accident and encourages anyone who knows anything to come to him if they don’t want to speak to officers. As the group begin to sing in choir, Danny spots Kieran on the edge of the crowd, and looks on at him in rage.

After the vigil, a Romanian family is seen arguing amid the crowd. Jackie approaches Kieran to ask why he’s here, especially as the family know he’s being questioned, but Kieran pushes back – saying he knows she wants to pin Nessa’s disappearance on him, but he had nothing to do with it.

She tells him she knows that Cefin was his child, which shocks him, and he demands to know who told her, but they’re interrupted by Deng, who asks Jackie for a word and praises her work while she was on the force.

Jackie quickly slips off when she sees Danny and Shell having a tiff that results in him driving off without his wife and kids, and she goes over to see what’s going on. Figuring he’s going to Spider Island to confront Kieran, Jackie recruits Cath to help her get there in time, while Bull spots the commotion and follows by car. By the time Jackie gets there, Danny is seated on an old sofa outside, clutching a shotgun. Cornered by other members of the community, he demands answers from Kieran about his relationship with Cefin – including if he had ever told him the truth about being his dad.

As Jackie begs Danny to put down the gun, Kieran tells him that he and Shell would meet in the woods sometimes so he could see Cefin, but they never told him the truth about his heritage. Danny breaks down, saying that he had suspected but never knew the truth, and it never mattered to him while Cefin was alive, but now he’s dead, he’s struggling for reasons to survive.

Turning the gun on himself, Jackie steps in and assures him that genetics don’t make a father – what Danny did for Cefin was more important, and he had every right to grieve because Cefin loved him. Danny breaks down in tears, creating an opening for Bull to grab the gun from him.

Reviewing the situation with Jackie, she tells Bull the reason he was in the woods the day Nessa disappeared was because he was meeting with Cefin, which at the time was still a sworn secret.

Kieran insists the woods were empty, and he never saw Nessa that day, but Jackie says six of the Bevan kids testified that they saw her there that day. He responds by saying six Bevan kids lied.

Jackie tells Bull that, with evidence being washed away every minute due to the flooding, and as the community trust her over him, they need to work together to crack both cases. Reluctantly, Bull agrees, and shares that – based on what James said to him at the beach - he and Cefin may have been at Solomon’s farm the day Cefin died. Shell, who has arrived to be with her husband, states that it is possible, mentioning there’s waste buried at a quarry on the edge of the farm.

When Bull and Jackie go to investigate the quarry, they find a large number of disused barrels.