Joel Reynolds (JASON BATEMAN) is the founder and owner of Reynolds Extracts, a small manufacturer of concentrated food flavorings. While he and his partner, Brian (J.K. SIMMONS), have to deal with various personnel issues -- such as line worker Mary (BETH GRANT) thinking new employee Hector (JAVIER GUTIERREZ) isn't carrying his weight -- for the most part, the company works quite well and is in the sights of a larger company that wants to purchase it.
That, of course, would allow Joel to retire and spend more time with his wife, Suzie (KRISTEN WIG), which is important to him since their lovemaking has completely stopped. While there are obviously various marital issues at play, some of that also stems from their neighbor, Nathan (DAVID KOECHNER), who's always wasting their time chatting about trivial matters.
But Joel's life begins to crumble when Mary momentarily refuses to work, thus leading to a chain reaction on the plant floor involving forklift driver Rory (T.J. MILLER) and fellow employee Step (CLIFTON COLLINS JR.) who ends up injured in the process. That not only eventually leads to ambulance chaser lawyer Joe Adler (GENE SIMMONS) showing up smelling a lawsuit, but also attractive small-time thief Cindy (MILA KUNIS).
Posing as a new temp, her goal is to get in bed with Step -- not literally since his injury was of the testicle variety -- but she ends up drawing the attention of Joel. His bartender friend, Dean (BEN AFFLECK), eventually convinces Joel that if Suzie cheated on him, it would be okay for him to cheat on her. Accordingly, and while under the influence, Joel agrees to have dimwitted gigolo Brad (DUSTIN MILLIGAN) pose as their new pool boy and see if she'll take the seduction bait.
From that point on, and as everyone ends up making bad choices, Joel's professional and personal life progressively unravels.