Tom arrives at the home where his wife Liddy is working in the kitchen at her grandmother's home. Grandma sics her dog on Tom, who manages to get past it and brings a large box into the kitchen. Tom wonders where Grandma is and Liddy admits she's probably upstairs counting her money. He shows his wife the dog bite and says he's brought a contribution to the home. Upstairs, Grandma watches suspiciously as Tom brings in Mister Muncher, a garbage disposal machine guaranteed to chew up anything. He dumps out a bag of bones to test it, and explains that he received the disposal in payment for a plumbing job. He hooks it up to the sink and then taunts the dog with one of the bones before tossing it into the disposal. The noise wakes up Grandma, who is trying to sleep up above.
That night, Liddy brings up food for Grandma's cat and dog. Grandma tells Liddy to shove it in through the chained door, and Liddy tries to apologize. However, her grandmother believes that Tom is trying to startle her into a heart attack. Liddy insists that Tom loves her but Grandma says that Tom only loves her money. Her granddaughter says she should put her money in the bank instead of her bedroom. Grandma insists she'll take care of her money, and that Liddy should have married a responsible man. Tom comes up and apologizes, and insists that she'll love it once she gets to know it.
The next morning, Tom is secretly placing bets and assures Liddy he'll go to his job interview. He notices a letter in the mail from a pet home and slides it under the door. Grandma picks it up, while below, Tom puts another bone into Mister Muncher. He then calls up to Grandma, saying she should come down and see her new "pet" and listen to it purr. As Tom recites the poem "Fee Fie Foe Fum" and talks about grinding bones, Grandma nervously takes a bonbon from one of several boxes.
Once Tom is gone, Grandma goes downstairs, telling her pets to run ahead. She examines the garbage disposal and hears it making odd gurgling noises. She sees a yellow feather and realizes that her canary is missing. When Liddy comes home, Grandma tries to convince her that Tom fed the bird into the garbage disposal and she's next. Liddy insists the bird just got loose but Grandma warns that Tom plans to kill her and grind her bones so he can get her money. Tom comes home and Grandma runs off. Liddy asks him if he killed the bird but Tom says that he cleaned the cage and the door must have come loose. He tries to yell an apology through her bedroom door but Grandma insists that he'll never get her money.
Later, Grandma takes care of her cat and dog and then watches as Liddy goes to work. Once she's gone, Tom starts chanting again and then finds the cat downstairs in the kitchen. He knocks on Grandma's door and says he's going to take care of the animals. Grandma looks through peephole and sees Tom walking away... with an axe. She eats more candy and listens as she hears Tom chopping at something in the kitchen. He then puts it into the garbage disposal as Grandma covers her ears in horror.
Once Tom leaves, Grandma runs downstairs and calls for her remaining pets. She examines the sink and finds fur in the disposal. When Tom and Liddy come back, she accuses Tom of being a murderer and Liddy has to wonder. Tom insists that Grandma is getting crazier by the minute, and suggests that she put the fur by the sink. He suggests that Grandma is trying to turn Liddy against. Liddy, in tears, doesn't know what to believe.
That night, Grandma leaves her room and goes to the kitchen. She addresses Mr. Muncher, demanding to know what he's swallowed. Looking beneath the sink, she finds a bundle and opens it. Inside is the axe, covered with dog hair. Going outside, Grandma goes to the garage where she's put her pets. She's muzzled the dog, and assures them that it won't be much longer until they can come back.
The next day, Grandma calls Liddy and Tom up and gives them $500 to spend the weekend at the night. She wants some time alone to mourn, and says she has some business to take care of. After making sure that Tom catches a glimpse of her suitcase full of money, Grandma says that she's going to donate it to the pet home. Once the couple leaves, Grandma brings her pets back home and pours blood on the sink.
Tom leaves Liddy at the mall and drives back home on his own. He hears the garbage disposal running and finds a lock of her hair and the blood on the edge of the sink. Grandma comes in and says she played a joke, She sics the dog on him and he slips on the blood and falls underneath the sink. As the garbage disposal starts up, Grandma advances on him with the axe.
That night, an angry Liddy returns home and calls out for Tom. She finds Grandma sitting in the kitchen with her pets, saying that she likes the garbage disposal after all.
The next day, the postman visits and notices that it's quiet. Grandma shows him that Tom and Liddy are leaving. Tom is frightened into shock, and Grandma waves goodbye to them and then starts feeding bones into the garbage disposal while inviting the postman to say hello to Mister Muncher.