The kids dare each other in a decrepit water tower which is mysterious in a number of ways: 1) Draining the water causes a powerful vortex, but the water level is not going down. 2) No one seems to work the bottom valve, but the vortex comes and goes. 3) It is absolutely impossible that anyone could swim through such a vortex, but Stu does. 4) The rotten roof breaks under the weight of little Billy (the ice-cream excess?) but carries his brother who weighs about 4 times as much.