HBO 'Girls' Season Four, Episode Five 'Sit In' Preview, SPOILERS & Plot Details: Who Is Mimi Rose? Adam Cheating on Hannah?

Enjoying Girls season four? Get ready for a lay in this week, because fifth episode "Sit In" is heavy... and spends a helluva lot of time on its very special guest, the mysterious Mimi Rose. The HBO show's last episode found Hannah Horvath (Lena Dunham) escaping Iowa and back in New York, only to find a new woman living in her apartment with her boyfriend Adam (Adam Driver). Her closest friends Marnie (Allison Williams), Shoshanna (Zosia Mamet) and Jessa (Jemima Kirke) are all in New York though, so perhaps Hannah will have some support as she figures out what's going on?

As pointed out in our recap of last week's episode, there's been drama aplenty already and, unsurprisingly, a lot of stuff doesn't seem to be going right for our brave foursome... especially when it comes to record company meetings or peeing in public!

Hannah, having been dealing with moving to Iowa and leaving Adam in New York, has returned only to find a new woman, Mimi Rose (Community's Gillian Jacobs) living in her apartment with Adam. Her TV's gone, her couch is gone... and Adam owes her some answers.

Unfortunately, it seems like they won't be ones Hannah will like.

Marnie, meanwhile, has been dealing with the stress of being the 'other woman' while struggling with her musical partnership with Desi... even while their sexual one was going gangbusters, but last episode Desi broke up with his girlfriend Clementine... so will the two of them be in the clear?

Ray, meanwhile, had a public meltdown, but patched things up with Shoshanna. Shosh, Jessa and Marnie, though, have all had some pretty epic struggles to start the season.

As HitFix's Alan Sepinwall pointed out, without Hannah around "the other Girls are each exhibiting the kind of self-destructive behavior of which we know they're capable, but which also seems like an unconscious way to fill the void she left behind."

In "" Hannah spends a lot of time under the covers in her former bedroom as her friends try to cheer her up... with varying degrees of success.

The best parts of the episode though? It definitely involves everything to do with Hannah discovering just what happened to the old wall in her room.

HBO's Girls season four, episode five "Sit In" airs Sunday Feb. 15 at 9 p.m. Are you excited? What did you think of the opening four episodes?

Check out the preview here.