Plot

The discovery of the murder scene leads Hardy and Miller to arrest a startling suspect in Danny's murder.

Hardy continues to irritate Ellie, especially when he gets her to sit in on Mark's interview. Mark explains his finger-prints were at the murder scene because he did some work there but key-holder Susan Wright denies letting him in and work-mate Nige destroys his alibi. However hotelier Becca Fisher comes forward to admit to an affair with Mark, thus giving him a new alibi. Following Steve's theory the police find that Mark does have a boat, stained with Danny's blood though Mark explains he cut himself on a fishing trip. Beth is approached by Steve, who tells her Danny was killed by somebody close to him, increasing her doubts about her husband. Meanwhile Karen, unable to get any locals to speak to her, tells Maggie and Olly she is gunning for Hardy after he failed to solve a similar case and Hardy tells his doctor he has taken on this investigation as a 'penance'. He does nonetheless accepts a dinner invitation with Ellie and her family.—don @ minifie-1

Evidence is beginning to point to Danny Latimer's father Mark as the killer. His alibi for the night Danny disappeared is weak - he was out with a mate but can remember his name - and the police has found his fingerprints in the seaside hut where they believe Danny was killed. Mark says that he had done some work there but that too is proven to be a lie. They learn Mark has a boat and find traces of Danny's blood. Hardy has DS Ellie Miller do the morning briefing, something she has never done before. Steve tells Danny's mother Beth that he has a psychic message for her from her son: that she shouldn't pursue the case as nothing will come of it and she knows the killer very well.—garykmcd

A flashback shows Mark Lattimer waking in the middle of the night and going to Danny's room where he finds the boy crying. He hugs and comforts him.

By the cottage on the cliffs Ellie meets with Alec, who speculates that the killer could have used a boat to deposit Danny's body on the beach without leaving any tracks.

In the morning, Beth Latimer looks at her belly in the bathroom. Mark interrupts her to use the bathroom and texts his friend Nige saying "You know where I was."

Karen White approaches Jack Marshall to try and get information but he rebuffs her.

Alec has Ellie give the morning briefing at the police station which she stumbles nervously through. They interrogate Mark who insists that the night of Danny's disappearance he was out drinking and eating with his coworker Nige. He also explains that he had been in the cottage at Briar Cliff a few weeks before to fix a broken pipe.

At the Latimer house, Pete asks Beth when Mark got home the night Danny died, which causes her to become suspicious.

At the marina, Ellie and Alec check Mark Latimer's boat and find blood stains in it. They also question Susan Wright, the woman who manages the cabin. She denies that Latimer ever got the keys to the cabin from her and denies that there was even a burst pipe. They also question Nige who confirms Mark's story. However, Ellie talks with his mother who says that Nige was in with her all night. When they confront Mark with the new evidence he maintains that he's telling the truth about the cabin and refuses to explain his whereabouts the night of Danny's death. He explains the bloodstains as being from a week or so ago when he had taken Danny and Chloe out fishing and Danny had stepped on a fish hook. Frustrated with Mark's intransigence, Alec arrests him for obstructing an investigation.

Feeling trapped in her house, Beth goes on a walk and tries to do some work at the paper but is quickly ushered out. She goes and sits on a bench by the cliffs and is approached by Steve Connelly who tells her that he has a message from Danny. Horrified, Beth runs off.

Karen and Olly approach Nige, who quickly hides a crossbow when he sees them. The ask him about Mark and he provides some basic information but quickly excuses himself citing work and drives off.

Alec interviews Ellie's son with her husband present. When questioned about how Danny got on with his father, Tom says that Danny told him that Mark sometimes "got in bad moods" and was occasionally abusive.

Beth and Chloe learn of Mark's arrest and Beth tells Chloe that they cannot trust Pete and must stick together. Chloe later texts someone about her father's predicament asking if they can help.

Alec meets with a friend and doctor who warns him about his health. Alec confesses that he hates Broadchurch and its people but came here because it was penance for his failure at Sandbrook.

Beth meets with Reverend Coates who asks about the possibility of a memorial service for Danny. Later she invites over Steve Connelly who passes on a message from Danny to not pursue the killer because it is someone close to her and the discovery of their identity would be painful.

Becca Fisher comes into the police station and tells Ellie that Mark was with her the night of Danny's death and that they had been having an affair. When confronted with her confession, Mark admits to the infidelity, saying that it was a mistake and the only time it has happened despite multiple opportunities he's been given.

Alec returns to the hotel where he's staying and sees Karen White. She angrily derides him for his failures in the Sandbrook case saying that "that family lacks closure" because of Alec's failure. She tells him that she's not going to let him do the same thing in Broadchurch.

As they lie in bed unable to sleep, Beth questions Mark about where he was the night Danny died. When he puts off telling her she asks him if she murdered Danny. Mark angrily denies it and then storms out. He goes down to the waterfront where he meets with Becca Fisher. She says that what they did was a mistake but Mark says that it wasn't for him. "If it wasn't then it is now" she replies. As the two hug the camera pans away to reveal Beth watching them stunned. That night out on the sea near the beach where Danny was found, a fire consumes a boat.