Red's swimming competition is interrupted by the Knobblies growing in the Fraggle Pond. Red uses Boober's Kohlrabi juice to poison the knobblies, but then gets a psychic "message" to "follow the roots." The roots lead her to Merggle Lake, home of the Merggles (a race of aquatic Fraggles). She learns that their tree is the center of all life and a probe into the unknown. Meanwhile, Doc and Sprocket start a campaign to prevent a nearby tree from being torn down during the mayoral elections by Herman Grubtoe.