The film is the story of a group of childhood friends brought back together by one of their number, Lucy (played by Missi Pyle), who planned a surprise four-day hike in the Montana wilderness to celebrate losing hundreds of pounds of weight after gastric bypass surgery.

However, Lucy quickly realizes while she has become thin and happy, her friends, played by Melissa McCarthy, Larry Sullivan, Phill Lewis, Josh Hopkins, Jack Noseworthy, Octavia Spencer, and Philip Littell, are miserable.

The film begins with a voice-over by Lucy (Missi Pyle) discussing what it's like being fat, and having skinny friends in college.

She asks Becky to rally all of the women's college friends for one final trip to see Lucy, who now helps run Holland Lake Lodge in Condon, Montana.

Becky brings her husband Richard and introduces him, for the first time, to commodities trader George, Grammy nominated rap producer Trevor, flight attendant Austin, and State Representative Raye who also brings his wife, Mary (Octavia Spencer).

Later at lunch, Lucy explains to her friends that she has had gastric bypass surgery and she remains four pounds away from her ideal weight.

Waking the group early the next morning, she informs them that they are going on a four-day hike in which she will drop her final four pounds of weight.