Casey and Derek's best friend, Sam, like each other. When Derek gets the feeling Sam wants to ask out Casey he conveniently lets Sam know about the Male Code which states siblings are off limits and step-sibs count. George and Nora don't think they know their kids.
Sibling rivalry heats up between Derek and Casey when Casey tries to help Edwin with his girl problem and Derek is forced to help Lizzie with her hockey. Both become too wrapped up in being a better big-sib than the other and forget about the needs of the younger siblings they are trying to help.
Casey is disgusted with her fellow students' apathy about the upcoming school election. Sheldon Schlepper expects to be a shoe-in, until Casey convinces Derek to lend his cool factor to the process by running himself.
Derek's band is so desperate for a singer that they ask Casey to join; even though she's more folk than metal and thinks they're a bunch of posers. George, remembering his rock 'n roll youth, longs to join the band himself
Casey, compromising all her principles, takes Derek's advice and lies when she desperately needs an extension on a school assignment. Soon she is trapped in a web of deceit and the harder she tries to extricate herself, the worse it gets.
To pay Derek back for his many practical jokes, Casey pulls a huge prank of her own: stealing the office furniture from the new uptight Vice Principal. Everyone assumes Derek did it. The only two people who know he didn't are Casey and Derek.
While Casey is freaking out about her upcoming dance competition and Derek is freaking out (by being annoying) about his upcoming hockey playoffs, Lizzie and Edwin decide they're sick of being the ever-accommodating middle-kids.
There are way to many bets stirring up at the Macdonald/Venturi household. When Derek makes a bet with Casey and she loses she is out to prove she can win and bets Derek that she can make a boy that is the opposite of her usual liking ask her out by Friday.
Venturi men are afraid of mice we find out when two mice inhabit their house. Casey's English partner, Kendra, has a thing for Derek, who shares this affection and tries to change his immature ways to impress her, only to find out that she likes immature boys. Casey uses the mice to get Derek and Kendra together when she finds out Derek really likes Kendra.
Casey invites her dad to dinner and tries to make it perfect. When it all goes terribly wrong and she breaks down crying in front of Derek the good guy in him comes out and he calls her dad to make things better.
When Casey is dateless, Kendra offers to play matchmaker. Casey gets angry when Kendra posts misleading fliers, however is content when Kendra tells her of her cross-referencing plan. Meanwhile, this is an open chance for Derek to throw a party. When George declines the request, Derek informs him it's a party for Casey to meet the finalists Kendra prepared for Casey to choose a date from, Nora has to intervene George's second response of 'No' to make the party happen. George and Nora promise to stay upstairs, but break the promise and come down to crash the party, and...