Sandy & Kirsten convince child services officials to let them become Ryan's caretakers, & Ryan agrees to stay out of trouble. But with the upcoming cotillion, an old-fashioned formal event at which teenagers make their "debut" in society, that may be hard to do. Reluctantly, Ryan is matched with an iconoclastic East Coast girl, Anna Stern (recurring guest star SAMAIRE ARMSTRONG); to his delight, Seth is paired with the dateless Summer (recurring guest star RACHEL BILSON); Marissa plans to attend with wary Luke; & despite some individual last-minute hedging on Sandy's & Jimmy's parts, all the parents agree to accompany their children to the ceremony.