This gives some plausibility to how Maxine got into the dome - she was already in Chester's Mill when the dome descended - though of course she could have been anywhere in the world on the other end of the phone connection to Barbie. And the phone call doesn't explain why we haven't seen her since then. Maxine says she was watching Barbie and Big Jim, but how come nobody saw her watching?
A big point in Maxine's favor, however, is that she's played by Natalie Zea, of not only Justified but The Following fame. This opens the possibility that Raylan Givens or Ryan Hardy may next show up under the dome - nah, I'm only kidding - but Zea does lend a punch to every role she plays.
Could she be the fourth hand? That's the title of this episode, and the question it ends on. Angie, Joe, and Norrie account for the other three, so who is the fourth? With any luck, it's not any of the many characters who have gone on to a better place beyond the dome - whether by stray or intended bullets or whatever reason - because getting their hand on the egg in the barn would be difficult. One place to look is into who has gone into a fugue and talked of pink stars falling, as Joe and Norrie and now Angie with the monarch butterfly on her arm have just done.
The surrealistic poker game continues, with the search for a fourth of a kind.