Mom and Dad find out about the big party Rodrick and Greg (Zachary Gordon) threw while they were away. They're furious, and punish them by grounding them for weeks, which means Rodrick can't perform at the town talent contest with his heavy metal band Loded Diper. Worse still, the band decides to go ahead and perform without him. Rodrick blames Greg for getting him in trouble, and torments Greg in every way possible.
On the night of the talent show, Greg's friend Rowley has no assistant for his magic act. Mom wants Greg to be Rowley's assistant. Greg agrees, on one condition: that Mom let Rodrick perform with his band. Mom lets a grateful Rowley perform.
Greg and Rowley's act goes horribly from a purely magical perspective, but it succeeds as a comedy bit, and everybody loves their performance.
When Loded Diper takes the stage and starts playing their heavy metal anthem, the audience hates them. But when the audience sees Greg and Rodrick's Mom dancing at the side of the stage in her odd, uncoordinated embarrassing way, the crowd goes wild and cheers loudly. Rodrick thinks his band is a hit, and is ecstatic. Greg and his Dad (Steve Zahn) decide to keep their mouths shut, rather than embarrass Mom and disappoint Rodrick.
Rodrick appreciates Greg getting him a chance to perform, and starts treating Greg nicely. Meanwhile, Greg has gotten friendly with his dream girl, Holly Hills, and starts to think having brothers isn't so bad after all.
Thanks John L!