A tenement backyard serves as both a lovers' dream garden and a battleground in Neighbors. It opens with a boy (Keaton) and a girl (Virginia Fox) on opposite sides of a fence. She passes a note through a knothole: "I love you." Keaton moons about in ecstasy, but his mother calls; he only has time to add "2" and pass it back. The girl's father (Joe Roberts) sees her kissing the note and rips it from her. He's horrified by the contents and sends her into the house. The note travels through the hole twice more, precipitating a fight about infidelity with both sets of parents.
While the parents are distracted, Keaton visits the girl by climbing her building. Roberts catches them, and Keaton goes out the window, slides across a clothesline to his own house, falls down the stair banister, and is propelled across another clothesline right into Roberts. The angry father hangs him upside-down on the line and pulls him back into his own yard, where he trades places with the rug his own father (Joe Keaton) is beating. After a solid whack that sends him up and over the line, his father unhooks Keaton headfirst into a barrel of rainwater. Keaton Sr.'s first extrication attempt merely breaks the barrel and Keaton is mired in mud up to his neck. As Roberts chortles, Joe Keaton thinks better of using a pick and tries pulling his son's legs. With a few twists he frees a muddy Keaton, who appears to be in blackface.
In retribution, Keaton smacks the person on the other side of the fence. Unfortunately, it isn't Roberts, it's a cop. The officer comes looking, but finds only a freshly cleaned Keaton doing laundry. He nicks a passing African American man, who escapes when the cop gets distracted by a kiddie craps game.
Thanks to a painter overhead, Keaton resumes blackface (the worker dumped a can of paint on him). The cop collars him. As he's marched down the street, Keaton cleans half of his face. As soon as he turns the 'white' side to the officer, he thinks that the prisoner has escaped. Keaton turns back and forth, confusing the cop terribly, then he disappears. After the cop leaves, Keaton climbs down from the telephone pole and runs into another cop. Despite a little dance to prove he's harmless, the second cop nabs him and takes him away. They pause at a ballpark fence and through the slats Keaton sees that Babe Ruth is at bat. The cop hauls him away, but the Bambino's home run sails over the fence and knocks the officer out cold. Keaton cheers the home-run king.
A third cop comes up from behind and Keaton falls down at the sight of him. Keaton's trip to the station resumes. He grabs an emergency banana off of a fruit stand, and they walk next to and African American woman with a covered cart. Keaton throws the banana peel in front of the cop who slips, then hops on to the cart, hiding under a white bedsheet. When the woman arrives home, Keaton arises, frightening the family with his ghostly appearance.
Next, the young inventor works on his 'patent fly swatter': a board mounted like a see-saw over the back fence gate. To test it, he wakes Roberts up with kicks and a hammer, then jumps over the fence. Roberts chases him through the gate, gets bopped by the board, goes back and gets hit again. While Keaton hides behind drying laundry, both fathers and three cops get whacked and indulge in mutual recriminations. Eventually Roberts reveals Keaton's hiding place and he jumps down, using the fly swatter to break his fall which sends his own father flying over the fence. The police chase after Keaton, who runs into Roberts' house. A cop mistakes kittens under a sheet for the fugitive. Meanwhile, a superintendent joins the police convention in the yard and the two fathers are hauled off. One officer continues to look for Keaton and discovers him atop an electric pole. When the cop throws rocks at him, he uses his clip-on tie to slide down a wire to the street: right in front of the paddy wagon. He joins the gang.
Everyone winds up shouting in court. Keaton takes Fox aside and proposes marriage. The judge (James Duffy) forces both fathers to sign a bond to keep the peace, which is immediately tested when Keaton announces the impending marriage.
Next, the family is seated around a table of wedding presents, including the essential How to Box by Jim Corbett. The male relations are armed with bats and bricks. The bride waits outside atop a trash can. J. Keaton has a broken arm, which he says was caused by Ford ownership. As Keaton dresses his suspender buttons pop off and he's left fighting to keep his oversized pants up. He joins the wedding party and he makes a speech about what he'll lose by giving up the single life. First gone are his trousers. The bride comes in, the minister breaks up a fight between Keaton and Roberts, and the ceremony begins. Keaton's pants drop, the minister's pants drop (Keaton stole his belt), then everybody sits down so that nobody's pants will drop. A guest gives Keaton a padlock, so he secures his trousers to his vest. Upon seeing the cheap ring that Keaton provided, Roberts calls off the festivities and drags his daughter home. Keaton tries to go after her, but his mother escorts him by the ear to his room.
The star crossed lovers speak to each other from their third-floor windows. With the help of two friends (The Flying Escalantes), Keaton rides a standing piggy-back across the yard to fetch her luggage, then her. Caught by the fathers, he runs away. One friend gets snagged by a clothesline and the other falls down a delivery hole in the sidewalk, leaving only Keaton and Fox to slide down a coal delivery chute to where their clergyman is shoveling coal. He completes the ceremony, then goes back to his chores as they embrace. — Lisle Foote