On Tom's seventh birthday, he tries to keep Jerry and an army of ants from taking away his birthday cake.
Tom is having his seventh birthday, which is being celebrated by his owner with a big vanilla cake that has white frosting and pink icing, which draws the attention of an ant, and later, Jerry. As Tom looks at the cake, blows out six if the seven candles on his cake, Jerry shows up to help with the seventh candle and grabs some icing off the cake. Tom chases him and launches him uses a floorboard as a makeshift catapult, which shoots Jerry in the air near a bush where the mouse is taken to an infirmary tent by the army of ants. General Ambrose B. Ant questions why Jerry is here, and learns that, Jerry has the objective as the ant army, acquiring Tom's cake.
The ants and Jerry plan an assault on Tom. Tom leaves the house and returns to the picnic table in the backyard to enjoy his cake. An ant approaches it, but as Tom grabs a fork to enjoy his cake, he spots the ant and swats him away with a brush and brushes away another. Jerry then tries to sneak off with the cake, but gets swatted as well. The ants begin their march up the table, but Tom counters with his slingshot, making the ants scatter. However Tom sees the ants coming from the sky. Tom takes his cake and floats out into the swimming pool on an inner tube. An ant in scuba gear, armed with a safety pin enters the pool to puncture Tom's flotation device. Tom recovers from the water while keeping the cake above water, and runs to the kitchen and tries to lock out his attackers.
Jerry distracts Tom a bit while the army of ants storm the house. Tom keeps the ants from entering through the kitchen's faucet, with a cork, Tom is outnumbered and the ants cut Tom's cake in eight pieces and took it in Jerry's mousehole despite Tom's best efforts. Tom then returns to an platter with only a few crumbs. When the owner is surprised that Tom ate every piece, and tells him that she'll make another next year. Depressed that he didn't get to eat his cake, Tom sits on the kitchen floor, sulking when a trumpet blasts and out of Jerry's mouse hole comes a piece of cake. The ants return a piece of his cake back to Tom and the ants sing "For He's A Jolly Good Fellow" holding letters spelling out "HAPPY BIRTHDAY TOM". As Tom starts to eat his cake slice, Tom sheds a tear of joy.
- It is confirmed that Tom turns 7 years old in this episode (according to the candles on his birthday cake); whereas in most other episodes, he is 6 years old.