Derek breaks up with Sally after she reveals her plans to attend a university in another province. Believing that he is hurt over what happened and is bottling up his feelings, a concerned Edwin and Casey try to get him to open up. Meanwhile, Lizzie and Marti attempt to keep a dog hidden from most of the family.

Casey is in panic mode after the diary that details her unsettling romantic dreams about Truman goes missing. Believing that Derek and Edwin took it, Lizzie and Marti attempt to get the diary back by making their stepbrothers' lives miserable.

A surprise visit from Edwin's friend Teddy turns into a frequent occurrence that makes the entire McDonald-Venturi household uncomfortable. Despite warnings from Emily, Casey decides to go out on a date with Truman.

To be eligible for college athletic scholarships, a "D" average Derek seeks George and Edwin's help in passing all of his final exams. Meanwhile, Nora and the girls try to get a stressed out Casey to stop over-studying and relax.

Derek serves as a chaperone for Casey who is going to a party in Toronto with Truman. Meanwhile, Lizzie goes out on a date with a boy that the family has never met.

As the prom approaches, Casey and Derek both find themselves without a date. Meanwhile, George and Nora have something to tell the family.

A worrisome Casey is having difficulty writing her valedictorian speech for graduation. Meanwhile, Edwin is concerned that he won't be able to live up to Derek's reputation at J.S. Thompson High when he goes there in the fall.