The loss of Rita's boat is quite sad; the boat appears to be sentient and waves goodbye to her as it sinks beneath the rapids.
Roddy hears strange sounds inside the house, slowly goes to look, and then sees a muddy eruption from the kitchen sink. But he doesn't see a mud-covered figure, looking like a monster, coming up behind him with its arms reaching out (but it turns out to be Sid who has no ill wishes toward him).
After Sid flushes him down the toilet, and he travels a long way, Roddy pops out of the system and finds himself far above the city, falling toward it. However, he turns out to be just a few feet above a sidewalk drawing (depicting an aerial view looking down) upon which he lands.
Spike, Whitey, and others chase after Roddy and Rita in her boat through the city on its "river." One rat bounces off a large float into another rat, while Spike ends up on the boat, standing on Roddy and preparing to stab him with a corkscrew or something similar (attacked to a line trailing behind him). Rita then hits the propellant, Spike's line goes taut, and he's yanked backwards off the boat, wraps around and slams into a pipe several times, and then lands on a pipe on his crotch.
Rita's boat goes through a river passage labeled as dangerous, and the rapids are rough as Rita battles with Le Frog. The boat then blasts out into an opening, with its mechanical arm grabbing a pipe above it. That results in the boat dangling vertically from it, with Roddy falling and Rita catching him (as she dangles from the end). Le Frog then dislodges the hand's fingers from the pipe, causing the boat to fall. But Roddy and Rita quickly create a makeshift parachute, with the updraft lifting them up and above Le Frog (although her boat crashes into the whirlpool below and sinks).
Roddy finds Rita tied up, dangling in front of a floodgate that's opening (and will allow a tidal wave of toilet water to wash over her and the city). Roddy then flies up to her on a balloon of sorts, with Toad firing staples at him (like a machine gun), eventually popping the balloon.