Bobby becomes an environmental activist and unearths Hank's long buried secret.
When Bobby's history teacher, Mr. McKay, inspires him to become more environmentally aware, he goes overboard handing out violations. Boomhauer gets one because his 1970 Cornet hot rod doesn't meet EPA standards. Peggy's busted for not recycling a battery. But the kicker is when Hank catches Bobby in the Strickland Propane dumpster - on a "field trip." Hank's violation lands him in the Tom Landry Middle School Environmental Court.
During court, Hank learns that the city plans to drain the quarry and make it a landfill. Normally, Hank wouldn't care - but draining the quarry would reveal a dark part of Hank's past. In high school, Hank, Bill and Dale took Boomhauer's prized Mustang for a joy ride and Dale accidentally drove it into the quarry - with all of their letterman jackets in the car as proof. They've never spoken of the incident and Boomhauer still doesn't know the truth.
The guys immediately join Bobby's efforts to stop the landfill project. When they lose the city council battle, Hank decides they only thing left to do is to retrieve the sunken car before the draining begins. That night, Hank, Bill and Dale drag up the car (and tons of other forgotten junk), but get caught by Bobby and Mr. McKay. Bobby tips off Boomhauer, who races to see his beloved car. Hank confesses everything, but winds up getting arrested as a protester. Meanwhile, Bill and Dale deny any involvement, but Boomhauer knows better.