Water gushing from a basement pipe leak causes a flood. Oscar dives in with his snorkel on to help.
Gordon and Susan are getting ready to go to sleep after a long day when they suddenly hear water gushing. When they look out the window, they see Ernie and Bert float by on their beds. While Susan rushes off to tell Maria and Luis about the flood, Gordon brings Bert and Ernie inside their apartment. As he and Susan try to settle them down to sleep, Luis and Maria tackle the water pipe leak in the basement. When Oscar pops in to "help," he startles Maria and the valve handle falls into the water. Oscar happens to have a snorkel on, so he dives under water to look for the valve handle which has a circle in the middle. First he pops up with a tricycle tire which is shaped like a circle, but clearly won't work as a valve handle. Then he pops up with an old flute. When Maria tries to use it as a valve handle, she observes that circles in the flute actually fit over the circle on the valve. Maria stops the big leak! Maria and Luis then turn to the plumbing blueprints to guide and help them fix the broken pipes. They see that a curvy piece of pipe is missing and Oscar once more dives down to see what he can find. After popping up with a straight paintbrush and a curvy straw which won't work, he finds a vacuum hose. Maria bends it into the right shape and uses it to fix the leak! Finally Ernie and Bert fall asleep as Maria and Luis come upstairs to tell everyone the good news and how Oscar helped save the day!