Life With Derek

Male Code Blue (1x13)

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Casey likes Derek's best friend, Sam, who has feelings for Casey too. 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 friends siblings (or step-siblings). Derek tries to break Casey and Sam apart but fails to do so.