Five friends who reunite in an attempt to top their epic pub crawl from 20 years earlier unwittingly become humankind's only hope for survival.

New York fashion designer, Melanie Carmichael suddenly finds herself engaged to the city's most eligible bachelor. But her past holds many secrets—including Jake, the redneck husband she married in high school, who refuses to divorce her. Bound and determined to end their contentious relationship once and for all, Melanie sneaks back home to Alabama to confront her past.