S3, E20: Will's (recurring guest Star William "Billy" Baldwin) return to the Upper East Side continues to stir up problems for Serena, Lily and Will's long-standing rival, Rufus. The relationship between Serena and Jenny is strained as a result of Jenny's deception. Blair spends time on the Columbia campus and realizes where she truly belongs. And Dan learns that Vanessa has been keeping yet another secret from him.