The Bay season 4 ending explained: Who was the arsonist?

In this fourth season, we've watched on as DS Jenn Townsend (Marsha Thomason) and her MIU team have investigated a truly head-scratching case of arson and attempted murder. But also, as the episodes have unfolded, we've found out that the case is not as straight-forward as it first appeared.

Is there something that connects the arson attack that killed Beth, the attack on Dean's yard and the discovery of a body on Frontierland?

The finale underlines that this is a complicated crime with years-long tension bubbling beneath the surface, both in regards to the case itself and the people around it. But who was the killer arsonist at the heart of the drama? Read on for everything you need to know about the ending to The Bay season 4.

The Bay season 4 ending explained: Who was the arsonist and killer?

We start off the finale in the wake of Jenn having a brick thrown through her family home window in the penultimate episode. Through the help of a neighbour's front door camera, she finds out that it was Lewis Walsh (Arthur Kay), who has been bullying Maddie and is also Terry's stepson.

We saw how, after a tense parent-teacher meeting, Lewis's first thought was about his mother relaying the information to Terry, so it's clear it's a fraught relationship and he's scared of his stepdad.

The mystery company that made a bid for the Frontierland site contract is also revealed. The name of the owner is Kim Walsh, who turns out to be Kim McGregor, Terry's wife and Lewis's mother, who has used her maiden name to ensure her husband could have two bids on the contract.

But of course, Dean still won that big contract even after the McGregors' two bids – so why did they want that job so badly?

When Jenn arrests Lewis for criminal damage of her home, Terry doesn't seem pleased to have to go to the station as his appropriate adult. But as they drive away, we see Carl (Karl Davies) watching on from behind the back door, clearly hiding.

Back in the police station interview room, we find out that Lewis's fingerprints are found on a lighter inside a car that was stolen on the night of the fire and parked around the back of the Metcalfs' house. So, was Lewis the one to burn down the Metcalf family home? It turns out, yes.

The teenager explains that he burned down the house to help Terry get back at Dean but when he admits to it, it's something that Terry disputes, saying that he never told Lewis to do so – but it's a little more complicated than that.

In a flashback, we see that Lewis was eavesdropping on a conversation between Dean and Terry, where Terry is shouting about losing the contract to Dean and the future of their family business. "If you had balls, you'd do something about it," Terry says. Lewis then admits to the police that he wanted to "show him what I was made of" to stop Terry feeling as though Lewis was useless and should disappear.

Elsewhere in the finale, Tony tells his ex-wife/new love interest Ellen that he can't move away with her and quit his job, even though she has now told her partner that she wants to leave him to be with Tony. But Tony almost runs out of their tense conversation needing to go back to work instead to have a meeting with his boss about cuts.

In that meeting, they tell Tony that he has "to make efficiencies" to his team but doesn't take lightly to the request, telling them about long hours, lack of resources and being over-stretched. The meeting is one that the team can hear from outside and Tony refuses to have the conversation with them about making cuts to his team. It's left pretty open-ended with Tony telling the team to just continue work as usual as the ball is now in their court.

In Jenn's personal life, Erin later returns home after her whirlwind of a day with her mum, which has cemented that she isn't the person she wants to live with after all. The locks on the front door are also finally changed, with the hope being that Jacqui can't just come and go again as she pleases.

Jenn then explains the case and Lewis's involvement to Maddie, who has been terrorised by Lewis at school. Jenn says that the morning he was fighting with Yousef, Lewis thought that Maddie had heard him talking about the fire and his bullying was an attempt to scare her into not saying anything.

Who burned down Dean's yard?

The team get a warrant to search Terry's home and business properties, but Carl comes into the station of his own accord wanting to speak about the fire at Dean's yard. The fire at the house had nothing to do with him, he says, but the fire at the yard was his doing.

It was spurred on by Terry's comments in the pub about Dean returning to work after Beth's death, which is a scene that made the father and son seem supportive of Dean in his time of grief, but actually only angered Terry further.

"If he finds what's there, it'll finish us," Terry later tells Dean and explains how they need to make sure Dean doesn't work that site. He hands him the petrol canister and while Carl was the one to set the yard on fire, it was definitely prompted by Terry, who is then arrested for conspiracy to commit arson.

The dead body found on the site was that of Daniel Hickson, a planning officer who was murdered and buried on Frontierland. It turns out that Frontierland was the same site that Terry's father's company was working at the time and the same site that Terry was keen to work on when the contract came up again.

A "family heirloom" gun is found on Terry's site, which was suspiciously hidden. The bullets are a match for the round that was used to kill Daniel and Terry then reveals that Daniel was privy to a backhander payment that would help his dad get the "prime jobs". But when Daniel threatened to blow the whistle, his dad then had to "shut him up or it would have ruined everything".

So, Terry's dad murdered Daniel and Daniel's body was found on Frontierland because it was "convenient" – just doing what he was told by his dad.

Even though Terry concludes that he had nothing to do with Beth's death, he is arguably the reason why Beth died. Lewis was only wanting to exact revenge on Dean because Terry was constantly talking about Dean ruining his career and business. Lewis has confessed and later on Jenn visits the Metcalfs to tell them the news of some of their closest family friends being involved in Beth's murder.

Izzy feels guilty because she feels as though Lewis only burned down their family home in retaliation to her embarrassing him at school over his crush on her. But Izzy had nothing to do with it – instead Lewis was only wanting to do what he did to seek approval and attention from Terry.

Jenn explains that if Lewis pleads guilty, he's looking at a minimum sentence of six years which doesn't sound like much because he's "still a kid", she explains. He'll be in a youth detention centre until he's an adult. Carl's willing to testify against his dad and Terry's facing a 10-year sentence for unlawful disposal of a body and attempting to pervert the course of justice.

We later see that even though Matt has said he'll no longer go to university in order to care for his siblings, Dean helps pack his stuff up, urging him to go, saying that he'll step up and care for the family. It's an emotional moment, with Dean telling Matt how proud he is of him and how much he misses Beth. We then later see the Metcalf family laughing and smiling, ready to move on now that the case has been solved.

The Bay season 4 continues on ITV1 at 9pm on Wednesday 15th March, with season 4 available to stream in full on ITVX. The Bay seasons 1-3 are also available to watch on ITVX and BritBox – you can sign up for a 7-day free trial here.

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