In-laws and the nouveau rich are mercilessly ridiculed in My Wife's Relations. The forward sets the action in a multilingual city where "people misunderstand each other perfectly." Keaton first appears pulling taffy. An immigrant couple telephone a judge, asking to be married in Polish. He says yes, as he speaks no other language. Meanwhile, Keaton plays jump rope with the candy and whacks a postman with it. The letters fly. Keaton runs out, discovers a letter stuck to the bottom of his shoe, pockets it, and ducks when the mail carrier heaves a bottle at him, breaking the Polish judge's window. Keaton takes off, colliding with an unattractive woman named Kate. She sees the broken window and drags him before the judge. The official asks (in Polish) if she'll take that man to be her lawful wedded husband. She says "Sure he broke your window " nodding. The judge speaks to a confused Keaton, whom the bailiff advises to nod. The couple sign the register and are congratulated. Then they see the certificate of marriage and Keaton, shocked, eyes his bride. She hauls him away by his lapel.
Daniel never entered a den like Kate's family's home: her father (Monte Collins) and four large brothers (Joe Roberts, Tom Wilson, Harry Madison, Wheezer Dell) await their dinner after each newly arrived brother tossed aside the last one's hat from the light sconce by the door. They thoroughly inspect the groom, examining his teeth, legs, and shoes as if he were a horse. (The verdict: "he won't last a week in this family.") They drop him unceremoniously on to the floor and belly up to the dinner table. After replacing the last hat on the sconce with his own, Keaton joins them. He attempts to eat his salad, but they keep him too busy passing food. Keaton gives up and pours coffee for Wilson, watching dumbstruck as he adds cube after cube of sugar. Keaton has a better solution: he pours the coffee into the sugar bowl, mashes it up a bit, and hands it to the happy in-law. Wilson has another problem when the spoon in the cup pokes him in the eye as he tries to drink. Keaton helpfully bends the spoon back for him.
Kate brings a pan of large meat chunks to the table and all but Keaton say grace with a fork in hand. Immediately after the prayer they all quickly stab a piece, leaving nothing for the groom. He notices the wall calendar: its Thursday. He pull the page off and tells his new family that its Friday. Good Catholics, they're horrified that they ate meat on Friday and they return it to the pan. Keaton takes three pieces and digs in.
Bedtime arrives, and a pajamed Keaton carries a mattress and bedclothes into a room and sets them on a convenient table. An angry Kate emerges from beneath. He sets them on a bed frame, but a broom across the middle turns it into a see-saw. He gets into bed and can't figure out why he's moving back and forth. Eventually the frame collapses. He falls on his bride and is promptly tossed back on to his broken bed. Meanwhile, his brothers-in-law use earplugs to cope with each other's snoring.
Later Keaton can't sleep. He wallops Kate several times and pretends to be asleep. She soon sees through his ruse and breaks a water pitcher over his head. The honeymoon is complete.
In the morning, Keaton lies unconscious among pitcher shards. Kate realizes that he's been out all night so she summons her family. They attempt to resuscitate him using techniques for drowning victims. Then Kate gets some pepper; a sprinkle doesn't work, but half the shaker rouses him and gives everyone sneezing fits. The family tosses Keaton around like a medicine ball, then the siblings depart for the kitchen.
Roberts finds the grimy letter that stuck to Keaton after his bout with the postman. He reads that the client must call and collect the $100,000 estate left by his late uncle. The family realizes that since Keaton is rich, they have to be nice to him. In the meantime, Keaton has offered to fight his father-in-law, who dispatches him with a kick to the chin. Awoken by an alarm clock, Keaton pulls a rug over himself and goes back to sleep.
Kate runs in, solicitously wakes him, plants a kiss on him, and skips back to the kitchen with him. Each family member hands him money, and Kate tells him to go rent a nice place. Stunned, Keaton lets them shake his empty sleeve while he uses his hands to count the cash.
They move from the alley to the avenue, where a maid brings coffee for Kate to slurp from the saucer as Keaton hands his hat to a butler. The family gathers for a photograph in their ill-fitting nouveau-riche finery. They concentrate so hard on looking at the camera lens that as the tripod sinks, so do they until they're on the floor. The photographer rights the camera and the pose. No matter where Keaton stands, the family pushes him out of the picture. He settles for the floor, quite like a dog. After the flash, they kick the photographer out the front door.
Next, Kate asks Keaton to put half a cake of yeast in the homebrew. He accidentally puts the whole box in and leaves the kitchen. The vat bubbles over wildly.
Guests arrive. One asks Kate how they could afford a home fit for a bootlegger. She shows him the grimy letter, but discovers the true address: Miss Rose Royce. She alerts the family and they decide to murder him first, then kill him.
Keaton comes back in and detects a chill. He runs out and through the suds-filled kitchen. Roberts opens the kitchen door and a wall of froth spills out. Keaton plays cat-and-mouse in the foam, then escapes. A chase ensues. Some in-laws heave bric-a brac and a real brick at him while he makes the circuit of the entryway, kitchen, and living room. He tosses one in-law off of a grand piano by opening the lid and stabs two with a coat rack. Back in the entryway, he bonks an intruding cop with a brick, then uses it as a pillow for him when he passes out.
Racing out the door, Keaton goes up the building's grand staircase with two brothers-in-law in pursuit. He runs up another flight then rolls himself back down in the stairway carpet, bowling over his pursuers. A workman sees the rolled carpet and he rolls it down the first staircase. Keaton tumbles out at the feet of the rest of the family. He runs upstairs.
Trapped between two in-laws coming down and the rest coming up, Keaton hops over the banister and pulls the rug out from under the lot of them. He's last seen relaxing on the Reno Limited train. — Lisle Foote