"Knock Knock Who's Ed?" is the 3rd episode of Season 2and the 29th episode of Ed, Edd n Eddy. In this episode, Edand his friends get thrown out of Ed's house while trying to prepare for a marathon of Ed's beloved monster movies. The Eds now attempt to find a place to watch the marathon.
The Eds, for their latest scheme to swindle The Kids out their allowances, build a crudely-built swimming pool of lime-flavored gelatine. However, as they're waiting for the gelatine to set, Ed decides to take a dip in the swimming pool and then swallows the gelatin, only for it to seep out between his teeth. Edd and Eddy, disgusted and disappointed, takes Ed home. At Ed's House, Edd and Eddy notice reminders all over his room about an 8-hour Cyclops Movie Marathon, as Ed explains further, Edd and Eddy decides to join Ed. Ed's guests, Edd and Eddy, demand for sustenance. Ed leads them to his kitchen, where Jimmy and Sarah happen to be painting, to get themselves a snack. However, Jimmy and Sarah aren't happy about their "intrusion" and Sarah demands them to leave. The Eds refuse to do so, prompting Sarah to eject them outside and lock them out.
The Eds attempt to get back in the house by dressing up as a giant dolly, however, they find themselves hauled on top of a traffic light by Sarah. Distraught, Edd suggests to Eddy they can head to their houses to watch the marathon, but Eddy refuses to do so, so they decide to try their luck at other houses. They decide to watch TV at Kevin's House by claiming that Ed was involved in an airplane crash and needs to heal at by watching his TV. Kevin sees through their poor plan and shuts the door on The Eds.
The Eds decide to visit Rolf's House for TV, but Rolf isn't to happy about their presence. As Rolf asks Eddy to leave, Edd points out one of Rolf's bizarre antiques, and Rolf begins to retell the story about his journey from The Old Country to Peach Creek, detailing about a "Giant Sea Cucumber" who'd claimed the life of his Great Nano.
The Eds soon excuse themselves to the bathroom, where they take a bathroom vent to the living room, undetected by Rolf. The Eds start up Rolf's rather dated television set and switch it to the marathon. Ed is immediately fixed onto the TV set, while Edd and Eddy remark over the show's cheap production values, but Ed angrily instructs them to sit down.
Rolf notices the Cyclops and remarks about how the creature reminds him of his Great Nana, but Ed angrily forces him to sit with Edd and Eddy for the rest of the marathon. Ed then tells him no more talking before going back to the movie. Rolf asks Edd how long must they wait and Edd states it is an eight hour marathon. Ed then yells at them to be quiet before going back to the movie. Ed then demands for some snacks before he goes back to the movie and the episode irises in on him.