Mare believes Erin was murdered by Billy Ross (Robbie Tann), her uncle and the presumed father of her young son DJ. However, a minute into the episode, we finally get a look at that mysterious photo Erin's bestie Jess (Ruby Cruz) found in her late friend's journal. The father isn't Billy, it's his brother John (Joe Tippett), who is also the one who killed Erin.
John tells Mare that Erin threatened to tell his wife Lori (Julianne Nicholson) about the affair if he didn't pay for DJ's ear surgery. She brought a gun to their late night meeting at Brandywine Park and planned to shoot herself if he didn't agree. He says, while wrestling over the gun, he accidentally shot her in the hand. He then panicked and shot her in the face.
John is very calm, cool, and collected as he lays out the details of what happened. How he and Erin used pre-paid phones to keep their relationship, which started at the reunion, a secret. But that night, she texted his real phone. How he called Billy to help him move Erin's body. How he convinced Lori to lie and say Billy was the murderer to protect their family. How he drove back to Mare's ex-husband Frank's (David Denman) engagement party after committing the murder so that he would have an alibi. It's a tactic that clearly worked since Mare believed he was actually Frank's alibi when she initially wondered if her ex husband could have killed Erin. To be fair, every man on Mare Of Easttown has been a possible suspect at one point or another.
John goes to jail for Erin's murder, asking Lori if she'll take in his and Erin's son. (Like, seriously, the nerve of this guy.) But Mare isn't convinced that the case is closed. She's still looking for the murder weapon. According to the ballistics report, it's a rare gun, a Colt Detective Special. The same gun old man Mr. Carroll received as a gift when he retired from the police force. The grieving widower tells Mare it went missing the night of Erin's murder and was returned sometime after. The only other person with access to the shed where he kept it was the boy who cuts his lawn: Ryan Ross (Cameron Mann), Lori and John's son.
It's then Mare puts it all together and you can see how upset she is knowing that she has to arrest her best friend's 13-year-old son for murder. But, this is part of the job. Protecting this boy would be a slap in the face to Erin, who deserves justice.
Ryan knew about his dad's affair with Erin. His dad promised to end it, but when Ryan found text messages from Erin on his dad's phone the night of Frank's engagement party, he went to get Mr. Carroll's gun. He only wanted to scare Erin out of ever seeing his dad again. But in his desperation to save his mom and dad's marriage, he ended up shooting Erin accidentally. He called his dad who, with Billy's help, moved Erin's body back to the park.
John's confession, which shares some similarities with Ryan's, was his way of protecting his son. He was willing to take the fall to spare him. Though, I'll most definitely argue it is his fault this happened and he deserves to pay for his indiscretions. Lori also knew Ryan was the killer. "I would have taken it to my grave, if you hadn't shown up," she tells Mare, sounding very much like a Scooby-Doo! villain.
While it's disappointing to know Lori lied to Mare, she isn't the villain of this story. Mare Of Easttown is full of parents trying to protect their kids from a harsh world. An impossible task, no matter how noble the effort. But Lori's decision to lie would have caught up with her young son, who was so clearly struggling with the guilt of taking Erin's life. (So much so that Reddit guessed Ryan was really the murderer.) Ryan had become violent and despondent. He was headed down a bad road, a path that unfortunately is all too common for those who grew up in Easttown.
Throughout the season, we see how the life in this small town has beaten this community down. Mare wasn't able to "save" her son or her young partner Det. Colin Zabel (Ethan Peters) or Erin, but she is able to save Ryan. By arresting him, she gives him a chance to start over. Ryan made a terrible mistake that he clearly regrets. By serving his time, he gets a second chance. He gets an opportunity to earn forgiveness from others and himself.
And that's what Mare Of Easttown was always about: forgiveness. It's about, as Deacon Mark Burton (James McArdle) tells his congregation, finding that "next level of healing" that allows you to forgive and forge ahead. To do that, you must take one step at a time. Hopefully, forward, but as Mare learns healing isn't always a straight path. You also need a community of support.
In the finale, Mare says that she'll never get past her son's death. The grief doesn't get easier, "you just learn to live with the unacceptable," she tells Mr. Carroll. "You find a way to live with it." That traumatic experience, compounded by the things she's seen on the job, is making her more empathetic to those suffering around her including her daughter Siobhan (Angourie Rice), her mom (Jean Smart), and Frank.
Therapy has definitely helped her find compassion for her son's ex girlfriend (Sosie Bacon) and her struggles with addiction. After finding solace in Lori, she is now her best friend's shoulder to cry on. A role reversal that might have seemed unfounded just a few episodes ago. Most importantly, Mare is working toward forgiving herself.
It won't be easy, but watching her go into that attic, a room she hasn't been in since her son's suicide, shows how much she has grown since we first met the hard-nosed vape-smoking detective with a hero complex. It's as close to a happy ending as one could imagine Mare of Easttown having. It might leave you believing in the power of forgiveness.