It's August 1981 and the last day of summer camp at Camp Firewood. Beth (JANEANE GAROFALO), the camp director, is trying to make sure that the day's activities - including the annual talent show - go off as planned, all while keeping a romantic eye on Henry (DAVID HYDE PIERCE), a local astrophysics professor whom she asks to come over and teach the kids a thing or two about science.
Meanwhile, the various teen camp counselors are in the throes of romantic quandaries and/or hormonal rage. It's not uncommon to see Andy (PAUL RUDD) and Katie (MARGUERITE MOREAU) engaged in full lip lock, with Katie too busy or oblivious trying to find nerdy counselor Coop (MICHAEL SHOWALTER) a last minute date to notice Andy fooling around with fellow counselor Lindsay (ELIZABETH BANKS).
The perpetually lascivious Victor (KEN MARINO) finds himself enticed by camp slut Abby (MARISA RYAN), while J.J. (ZAK ORTH) is interested in finding some woman to help fellow counselor McKinley (MICHAEL IAN BLACK) lose his virginity. He seems interested, however, in Ben (BRADLEY COOPER), one of the drama counselors who works with Susie (AMY POEHLER), the uptight coordinator of the pending talent show.
Among the adults, 34-year-old Gail (MOLLY SHANNON) is lamenting her recent divorce and receives guidance and advice from Aaron (GIDEON JACOBS), one of her young charges, while camp cook and resident psycho Gene (CHRISTOPHER MELONI) torments both himself and his kitchen assistant, Gary (A.D. MILES).
As the day wears on and the big talent show looms - as does a falling piece of Skylab that's targeted the camp - everyone there tries to get in their last bit of fun and love before having to head back home for the fall.