When everyone is brainwashed and the park is destroyed, Mordecai and Rigby have to bring everyone back their old selves so they can prevent a highway from being built over the park.
Mordecai and Rigby take over the duty of judging the Park's Pie Contest, but realize that the job isn't all that easy when they find out that they have to pick a winner.
Margaret is transferring to another college, so Mordecai, Rigby and Eileen plan a going-away party at the park's abandoned ballroom, still haunted by its past hosts.
Mordecai and Rigby buy a potentially deadly sandwich at a restaurant, but when Benson falls ill after he eats it himself, they must set out to find the cure before he dies.
While camping out in a cave, Mordecai and Rigby accidentally melt a caveman frozen in a block of ice. When they try to keep him, Benson requires that they make him more civilized.
Mordecai and Rigby help their favorite '80s sitcom star, RGB2, escape from the studio lot and into the mountains to get out of a contract that has trapped him into staying on the show.
Muscleman, Mordecai and Rigby help "Donny G", a famous D.J. take back over the corrupt local radio station so Muscleman can play his song he wrote for Starla on the radio.