At Low Bar, Whitney announces to everyone that her half-sister will be visiting tomorrow. She tries to explain the complicated web that is her family tree, but everyone is at a loss to understand her complex family history. Nonetheless, they're excited to meet Whitney's sister.

Whitney's sister, Danielle, arrives at the apartment. Alex is excited to hang out with Whitney's sister, but Whitney wants some quality "sister time" first. Danielle asks Whitney to come to a doctor's appointment with her tomorrow morning because she wants to have a sex change operation.

Back at the bar, Mark and Alex wonder why RJ is late to work. Mark tells Alex that RJ broke up with his girlfriend last night, and Alex knows exactly where he is. They head to RJ's apartment to find him sulking in a bubble bath, devastated by the breakup. Alex and Mark manage to cheer RJ up.

Lily and Roxanne arrive at Whitney's apartment, and Whitney and Danielle tell them about the sex change operation. The next day, Whitney breaks the news about Danielle to Alex, who is confused but accepting. Meanwhile, Alex, RJ and Mark head out for a guys' day, but Alex and Mark quickly realize that RJ is trying to spy on his ex-girlfriend.

At the doctor's office, Danielle gets a consultation from the doctor. Whitney is appalled by the risks associated with a sex change operation. Whitney and Danielle get into an argument and Whitney storms out of the doctor's office. Meanwhile, RJ confronts his ex-girlfriend, and she tells him that she broke up with him because he forgot her birthday.

Danielle returns to Whitney's apartment and apologizes for the argument. Whitney also apologizes and tells Danielle that she's just concerned about her sister's safety. Alex arrives with a gift for Danielle: her first shaving kit.