Dean and Cas go on a hunt (with Sam assisting) where they have to pretend to be married to catch the monster. Exactly what it sounds like: a fake marriage fic featuring cooking, babysitting, drunken confessions, and one out-of-control game of Big Gay Chicken.
Set in S5 after 5x03. Dean wakes up in an alternate universe, only to find that he's stuck in (Sam's) terrible life. Only this time, it's courtesy of Lucifer, not Zachariah, and Dean (and Cas) are aware of what's going on, though Sam's clueless. As they try to find a way to help Sam learn his "lesson," or whatever, Dean realizes that things in Zachariah's version of this warped reality weren't as simple as he thought. Cas was there too, apparently, though Dean doesn't remember it, and he has a feeling there's something else that Cas isn't telling him.