Tom is chasing Jerry around Mammy Two Shoes, while she is yelling out confusing instructions on where to chase Jerry. She has a broom ready to hit Jerry but instead, she hits Tom on the head causing Tom to forget who he is and he believes he is a mouse. Mammy asks Tom if he is okay but he starts to squeak she becomes scared and jumps onto a kitchen chair. Tom terrorizes Mammy by shaking the chair causing her to fall off it, then quickly flees from the deranged cat.
Tom then heads over to the refrigerator and grabs a piece of cheese, before entering Jerry's mouse hole. Tom then moves into Jerry's small bed causing it to break underneath him. Jerry, who finds Tom even more annoying as an over-sized 'mouse' than as a cat, then overhears Mammy on the phone talking to the doctor about Tom. He hears that Tom is suffering from amnesia. Seeing Tom approaching her with mischief on his mind, Mammy cuts her phone conversation short and attempts to evade him by walking away on stilts. Tom pulls the stilts from under her causing Mammy to fall and he runs back into the mouse hole.
Jerry then runs to get the medical encyclopedia to learn more about amnesia. He reads that "memory can be restored by a sharp blow on the head". Jerry whistles and gets Tom's attention with a piece of cheese. Jerry then hides behind a curtain with a baseball bat. Tom starts searching for Jerry and every time Jerry swings to hit Tom, Tom coincidentally moves out of the way, exhausting Jerry. Jerry then tries dropping a bowling ball onto a piece of wood where a piece of cheese is sitting. Tom comes out of the mouse hole and eats the cheese. Jerry drops the ball, launching Tom headfirst into the ceiling. This cures him of his amnesia, but when Tom lands back onto the wood, the bowling ball flies into the air and falls on his head, sending him back to his mouse-like state.
Jerry then puts down a trail of cheese for Tom and he tries to drop a vase on his head. He misses. Jerry sets down another trail of cheese that leads under the piano. Jerry has tied a string to the piano leg and when Tom walks under the piano, Jerry pulls the leg out of the piano causing it to fall. Again, Jerry's attempts miss. Tom continues the trail through a door and an iron barely misses him as well. Tom reaches a big piece of cheese and Jerry cuts a rope tied to an anvil. But the anvil cuts off the back of his skin and crashes through the floor, again missing him. Jerry sits down disgusted, he's tried everything. Tom then gives Jerry a piece of cheese, but Jerry doesn't want it and throws it away. It lands in an egg cup on the shelf, which rolls and knocks a dish, which rolls into a laundry basket and into the broom. The broom falls over and releases a door which holds the ironing board which hits Tom on the head curing him of his amnesia. Jerry lets out a happy scream and runs to his mouse hole. He kisses Tom and then lies down on his bed to relax.
Tom also lies down right outside Jerry's mouse hole. Jerry looks outside and sees Mammy (who's unaware that Tom is back to normal) reading the medical book and holding a baseball bat whilst creeping stealthily towards the sleeping cat. She says she is going to cure Tom of his amnesia with a blow to the head. Jerry motions to stop her but she hits Tom anyway, unknowingly bringing his amnesia back. Jerry returns to his mouse hole whilst Tom, after once again dealing with Mammy, re-enters the mouse-hole, and returns to his mouse-like state. Tom gets the mouse kissed, before he knocks Jerry out of his bed, lies on that bed and makes it break again, leaving Jerry frustrated.
- Mammy's voice is re-dubbed by Thea Vidale when shown on Cartoon Network and its sister channel Boomerang. In this redubbed version, Mammy's line "It says here, a sharp blow on the head is a sure cure for amnesia. And that's what's he's gonna get!" as she sneaks towards Tom near the end of the cartoon for some reason has been muted out.
- When Tom transforms into a mouse-like state as the result of amnesia, the notable physical changes the deranged cat undergoes are the following; his head and ears becomes more rounded, his tail becomes slightly longer than normal, and has visible buck teeth protruding from his upper jaw.