After Barbie gets all of his aggression toward Sam out of the way and Pauline finds out that Sam murdered Angie, they start looking for the red door. The computer nerds start searching for all the red doors in Zenith, but stop when Barbie recognizes the door in Pauline's painting and tells them that it's in his backyard. Everyone saw that coming, right? Okay good, moving on.
The ones who made it out of the Dome sneak onto Don's property with Hunter in tow and head down the red door in the backyard before Don's men find them. In the root cellar, they find a passageway which leads to the tunnel and head through. Once in the tunnel, Sam, Barbie and Pauline encounter a swirling smoke that makes them see different things. Sam and Barbie have flashbacks: Sam remembers the day of Pauline's funeral when lil' Junior asked him to save him and take him away from Big Jim; and Barbie remembers the day the root cellar door was painted when he was little, and it turns out that Melanie was there that day and promised little Barbie that she'd see him again one day. (Huh?!) Pauline, on the other hand, has a vision; she's standing in the crater where her friends found the egg and Melanie appears to her and tells her that this is where it all began and that is where it must end.
Suddenly, all three of them are floating in the lake. Hunter is there too, but he wasn't special enough to have a flashback. Lyle, again, is missing (someone needs to put a tracking monitor on him). Once they get back on land, Barbie sets off to find Julia and Pauline sets off to find Junior. Sam wants to go with her, but Pauline says no and tells him to talk to Hunter and find Lyle because they need him.
Pauline returns to her old home and starts looking around. As she is exiting her son's room, she runs into Big Jim, who is obviously surprised to see her. The episode ends with Big Jim saying Pauline's name in disbelief. I'd be lying if I said I wasn't at least somewhat excited to see what comes next because while we don't know what's going to happen (who knows with these writers), we do know that Dean Norris is going to act the hell out of his character's first scene with the wife he thought was dead. And watching Dean Norris act the hell out of a scene is always fun.