Toby's self-harming, manic-depressive younger sister.
She's sparky, amusing, dangerous, sexy, and rude to the Feddens' friends. When "up", she is a loose cannon, speaking the truth where no one else dares.
Her increasingly heavy dosage of lithium suggests that the Feddens desire to silence these "eccentric outbursts" and maintain the family's fragile status quo. She is the family's conscience, and when events reach breaking point, it is Catherine who exposes the lies that both the family and Nick have been living.
Catherine is a beguiling, damaged and needy character, with a string of disastrous relationships behind her. She forms the closest bond to Nick because he is intelligent and sensitive enough to understand her. Yet it is she who finally betrays him.
