Life with Derek is a half-hour comedy series about a modern blended family, with two type-A 15 year-olds, Casey (Ashley Leggat) and Derek (Michael Seater). Each episode is an alpha-teen comic war between two self-obsessed teenagers in a take-no-prisoners fight for control of their house, their school, and their world.
Since Derek (Michael Seater) already has a girlfriend, Casey (Ashley Leggat) is shocked when he asks out a friend of hers. She tries to get him to do the right thing before she does it for him.
George (John Ralston) and Nora (Joy Tanner) plan a joint birthday party for Lizzie (Jordan Todosey) and Edwin (Daniel Magder). It's a fiasco until Casey (Ashley Leggat) and Derek (Michael Seater) reluctantly provide emergency help.
After Derek (Michael Seater) breaks up with Kendra (Lauren Collins) so he won't have to buy her a Valentine's Day gift, Kendra asks Casey's (Ashley Leggat) crush Max (Robbie Amell) to the Valentine's Day dance.
Derek (Michael Seater) turns out to be the world's worst babysitter, so Edwin (Daniel Magder) invites his friend Teddy (Cameron Ansell) over to stir up some trouble.
When Edwin (Daniel Magder) gets picked on by a schoolyard bully, he goes to Derek (Michael Seater) for advice, inadvertently causing Derek big trouble of his own.
Casey (Ashley Leggat) is shocked when Derek (Michael Seater) is selected to be a prefect at school and sets out to prove he's not the man for the job; Edwin (Daniel Magder) and Lizzie (Jordan Todosey) are jealous that Marti (Ariel Waller) always gets her way.
George (John Ralston) and Derek's (Michael Seater) mother Abby (Jennifer Wigmore) are dismayed Derek (Michael Seater) is failing Spanish and decide he should live with Abby in Spain for six months.
The family stages an intervention to convince George (John Ralston) to buy a new car; Derek (Michael Seater) faces the scary possibility of spending his 16th birthday at home with his family.