There is no “missing gun” plot hole in the Mare of Easttown finale despite many fans taking to social media to debate the fact. Decider put together a well-written article about the fact, but it’s something you can also figure out for yourself if you go back and rewatch the episode, listening carefully to the dialogue in the scene between Glen Caroll and Mare Sheehan.
As we know, Mare started to feel a little uneasy about arresting John Ross when he described the murder weapon as a normal gun, when in reality, Erin was killed by a Detective Colt Special.
Later, she gets a call from Glen who tells her he previously noticed a few things missing, including his Detective Colt Special, although it was returned before he could report it gone.
If you remember back in the first episode, the Carrolls called Mare over because they thought they heard a prowler outside. Well, at the time, Glenn went out to the shed to make sure he had the gun in case the prowler came back. He knew it was there that morning.
Mare of Easttown finale: Glen explains how he knew the gun was missing, there is no plot hole
Then later, he heard a noise out in the shed, which was likely Ryan going to steal the gun. Glenn checked and noticed that the gun was missing. He didn’t realize that it had been returned until later, which isn’t a plot hole. It doesn’t affect the story for Glen to have not realized when it was returned so long as it was after Erin died.
So, in summation: Glenn saw the gun in the morning. Ryan took the gun at night. Glenn heard Ryan in the shed and went to go see what the noise was. He saw the gun was gone because Ryan had taken it. Ryan later snuck back in and put it back. Then at some point after, Glen saw the gun was back.
This is the exact dialogue from the episode:
“Do you remember the morning you came over for my granddaughter and the prowler? Well I’d gone out to the shed and got the gun, so I know I had it then, but that night I heard a noise out in the shed, and I went out to get it and it was gone.”
The first season of Mare of Easttown is now streaming on HBO Max.