Only three of Popeye's nephews appear in this short.
Olive Oyl and the nephews are preparing a surprise birthday party for Popeye. For starters, the boys are shooting holes into doughnuts, which fall into hot oil, and blow bread and lunchmeat through a fan's spinning blades to cut them into sandwiches. Olive, on the other hand, mixes vanilla and chocolate frostings into checkerboard patterns for a cake.
Unfortunately, Popeye is coming early, so Olive tells the boys not to let him in until she says so. They pretend to be locked outside, so Popeye tries to help, but they stop him by giving him an electric shock then using a hose as a large rubber band to hurl a piano against him.
A running gag is, when the nephews ask Olive, "Can we lets" - "him in now," - "Aunt Olive?", she says, "No. Not yet, boys." First, it happens while she makes Popeye-shaped accordion-folds, and later when she is tying a ribbon on a gift.
Later, the boys set up a fake door and a "Welcome" mat to trick Popeye, and he gets punched by a spring-loaded boxing glove. He then tries to go down the chimney, but the nephews set off a big rocket. Ultimately, he ends up getting washed through a washboard and hanged up to dry with his spinach, so he wrings spinach into his mouth to gain extra strength. He proceeds to lift up the house, but then finds a surprise birthday party prepared for him, much to his amusement.
- Popeye's Mirthday at the Internet Movie Database