Emily dating kasey
Derek is opposed to a relationship between his best friend and his stepsister so he tries to sabotage the possibility of them coming together by informing Sam of the "Male Code", which says a guy's best friends cannot date their siblings (or step-siblings).
Derek tries to break Casey and Sam up but fails to do so.
The Mc Donalds and the Venturis kids (Casey and Lizzie vs Derek, Edwin, Marti) decide that the best places in the house aren't big enough for the two families, so they agree to decide by games of chance (dice, cards, etc).
When Casey sprains her ankle because of Derek, she gets whatever she wants(including the chair that Derek always sits in, and his tickets to a White Stripes concert) and Lizzie does everything for her, making Derek jealous. Derek dyes the white clothes pink, uses the neighbor's pool and stomps on their flowers, Marti makes "potions" with Casey's perfume and shampoo and hits the neighbor's son.
Meanwhile Edwin and Lizzie team up to "observe," spy on teenage behaviour.
Edwin finds out that every time Sam breaks up with Casey, Dereks team loses the game, but when they're together they win.
Casey tries to get rid of Derek for the dinner party she has planned with her biological father.Living-room redecorating creates strife within the family, as Casey, Lizzie, and Nora want to add a feminine touch to the household, while Derek, Edwin, Marti, and George are perfectly fine with the way the household is.Casey discovers she has a reputation as a grade-grubber and wants to rid herself of it by choosing a slacker to work with on a group assignment – like Derek.She asks Derek for help on how to lie to her teacher to get an extension, but those lies tangle up so far, that the teacher ends up sitting on her couch in her house. When Casey gets attracted to Scott, Lizzie's soccer coach , he asks her out. Derek feels guilty after hearing from Scott that he's dating other soccer sisters.
Meanwhile, George is upset after Nora says that she did not feel love at first sight with George.
Derek and Casey have a competition with who is the best sister or brother.