In the fictional small town of Ashton, a degenerate low-life alcoholic named Ron Bell is eaten alive late one night by a large swarm of slugs in his living room.

The following day, health inspector and sewer manager Mike Brady and Sheriff Reese head to Ron's home, preparing to deliver an eviction notice, only to discover his near-skinless body.

As he thrashes about in pain, Harold accidentally knocks over some of his chemical jars, causing a fire which ignites a tank of gasoline, resulting in an explosion that kills him and his wife Jean.

Don theorises that the slug's aggressiveness may be a result of chemicals being leaked into the sewer from a long-abandoned toxic waste dump that exists close by to the town.

Meanwhile, whilst dining at a restaurant, an unwell David begins profusely bleeding from his nose and collapses, before multiple blood flukes abruptly burst from his eye sockets.

Mike reunites with Kim as the emergency services arrive, whilst unbeknownst to rest of the town, a singular live slug writhes ominously on a vent cover.