Plot
Suburban homeowner Ray Peterson is home on a week-long vacation. Late one night, he hears strange noises coming from the basement of his new and reclusive neighbors, the Klopeks. Ray and his other neighbors—nosy Art Weingartner, Vietnam War veteran Mark Rumsfield and teenager Ricky Butler-suspect that the Klopeks may be ritualistic murderers. On another night, they observe the youngest Klopek drive an oversized garbage bag to their curbside garbage can and aggressively mash it down. Later that night, during a rainstorm, Ray sees the Klopeks digging in their backyard. In the morning, Ray, Mark, and Art search the garbage truck for human remains after the Klopeks' trash is collected but find nothing.
Mark's wife, Bonnie, finds their neighbor Walter's dog, Queenie, running loose. Worried about Walter, Ray, Art, Ricky, and the Rumsfields enter his house and find overturned chairs and Walter's toupée but no Walter. Ray collects Queenie, leaves a note for Walter, and sees one of the Klopeks watching him from their house. Ray and Art theorize that the Klopeks used Walter as a human sacrifice, becoming further convinced when Ray's dog Vince digs up a human femur from along the Klopeks' fence line.
Ray's wife, Carol, tired of the men's behavior, organizes a welcome visit to the Klopeks. While the Petersons and Rumsfields meet Hans, Reuben, and Dr. Werner Klopek, Art snoops around the Klopeks' backyard and is chased out by their dog. Afterward, Ray reveals to Art and Mark that he found Walter's mail and toupée at the Klopeks', proving they had been in Walter's house.
The next day, Ray sends Carol and their son, Dave, to visit Carol's sister. When the Klopeks leave, Art and Ray enter their backyard to search for Walter's corpse while Mark acts as lookout. Finding nothing in the yard, Art and Ray break into the Klopeks' basement, discover what appears to be a crematorium, and dig into the floor in search of human remains. Ray strikes a gas line with his pickaxe; Art escapes before the house explodes, and Ray emerges from the inferno just as Carol and Dave return home.
Walter arrives home during the commotion, having spent a few days in the hospital due to heart palpitations. He had asked the Klopeks to collect his mail for him, and they had mistakenly gathered up his toupée as well. When Art intends to continue looking for evidence against the Klopeks, Ray goes on a tirade, declaring that he and the others were wrong before climbing into an ambulance. Werner enters and accuses Ray of having seen a human skull in the basement furnace, revealing that the Klopeks murdered the previous homeowners, the Knapps, so they could live in their house.
Werner attempts to lethally inject Ray as Hans drives the ambulance away. Their struggle causes the ambulance to crash into Art's house, ejecting Werner and Ray, who makes a citizen's arrest. Ricky uncovers human skeletal remains in the Klopeks' car trunk. The Klopeks are arrested, and charges against Ray are dropped. While Art speaks to a TV news crew and explains how suburbanites are out to get criminals in their neighborhoods, Ray states that he and his family are going away for a while and asks Ricky to watch over the neighborhood.