Kate is out of her element in Allison's chemistry lab when she poses as her sister, who cut class to go out with a college guy.

Kate challenges shy Allison to enter a dance contest with her, but when Kate sprains an ankle, Allison must go it alone in the finals.

Miffed at Kate for signing them up for a twin-testing project, Allison moves in with Beth, vowing to find her own identity---and to celebrate her birthday without her sister.