Arnold and Helga perform a science project in which they're locked together in a greenhouse for 24 hours, but Helga's only looking for an easy A.
Stinky and Phoebe are presenting their school project, the subject being classical conditioning (Phoebe would ring a bell, and give Stinky a Mr. Nutty candy bar every time, causing him to drool whenever he would hear a bell ring). Arnold and Helga are to present their project the next day, and Arnold explains to Helga that they'll live inside the Sunset Arms' greenhouse from the time they get out of school, till the time they have to go in the morning. At the Sunset Arms, they enter the greenhouse, and immediately Helga asks where the electrical outlets are, but Arnold tells her there are none.
She plans on leaving, but Arnold plays on her need to seem tough, and convinces her to stay. While Arnold conducts an experiment on a potato (planting a seed in it and seeing if it sprouts), Helga reads comic books and eats all of her candy bars. When she asks where the rest of the food is, Arnold refuses to let her eat his potato, and offers his celery juice, freeze-dried kelp and trail mix, which she refuses. Helga tries ordering pizza, but it is consumed immediately by Abner. Arnold also experiments with having two different plants in the same pot, and two ants in the same ant farm: one black and one red, the latter Arnold requested earlier that Helga bring.
He describes the ants' behavior, which angers Helga further. Night falls, and Helga is unnerved when told that there are no lights in the greenhouse. When getting into bed, Helga's luxurious, inflatable bed pops when she jumps onto it. After brushing their teeth, the faucet drips throughout the night, keeping Helga awake. Arnold wakes up to find Helga eating his potato for breakfast, and gets mad at her, causing Helga to divide the greenhouse down the middle.
Arnold observes Helga, much like one of his experiments, causing her to throw a ball, which causes the ants to escape. Arnold saves them from being smashed by Helga, and Helga tries to stop the faucet dripping, but ends up beaking it, causing the greenhouse to flood. They try to get help, but Grandpa thinks they want more water. The greenhouse floods, but they float on Arnold's bed, and the ants float on the potato. The door eventually breaks from the pressure and frees them. They rush into Miss Slovak's class, and present their project gatherings (essentially a synopsis of the episode), and end with saying despite the torture, they had a good time.
Helga shows no excitement in working with Arnold whatsoever, despite being secretly in love with him.
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