Phil struggles with the return of his younger brother Mike Miller. Mike tells the group embarrassing stories about Phil, including his nickname, "Skidmark." Phil still holds resentment over Mike having hooked up with Christine, a woman that Phil was in love with.
Mike throws a bonfire party to celebrate the group taking him in. He serenades everyone with a rendition of "Spaceman" that reduces everyone (except for Phil) to tears. Everyone loves Mike and thinks he's hilarious, including Carol.
Meanwhile, Gail, Erica, and Melissa each separately turn down Todd's offer for a four-way relationship, needling him about thinking that was a good idea.
Later, Gail and Melissa talk. Gail apologizes and tells Melissa she didn't mean to hurt her. They each realize that they care deeply about Todd. They speak with Todd and tell him that they want to give the polyamorous relationship a go, where each of the two of them date Todd but not one another. Todd starts to propose to both of them but they stop him. They all group hug.
Phil attempts to upstage Mike's party and reclaim the love of the group by throwing his own party the next day. Everyone shows up late because they'd all been having fun at a "pre-party" that Mike threw. Phil performs a terrible rendition of "We Didn't Start The Fire," changing the words to personalize the song. Mike jokingly begins dancing along, getting everyone to laugh.
Phil gets angry and rails against Mike, trying to get everyone to understand that Mike isn't perfect. Phil goes too far when he brings up the fact that when their grandmother was dying, everyone was with her -- except for Mike, who went on a kayaking trip. Mike gets sad and leaves.
That night, Carol lectures Phil about being so mean to his brother, when they are the only two people in the world who have family left. He agrees to apologize to Mike the next day.
The next morning, Phil wakes up and realizes that Mike has shaved half of his head -- his head, beard, and one of his eyebrows. He goes to confront Mike.