Therese is the owner of the Asylum nightclub and the self-proclaimed Baroness of Santa Monica. She resents her sister Jeanette for her flamboyance and promiscuity (despite being a vampire and technically undead). At the Asylum, Jeanette handles PR while Therese takes care of the business end. Jeanette makes a point of flirting with everyone including the player, while Therese works hard to attain power and the favour of the Camarilla. She is a Malkavian with pretensions to be a Ventrue (visible in her affected distaste of the Nosferatu).
When the player meets her she is in a feud with Bertram Tung, a Nosferatu elder, that the player must persuade her to call off. She is constantly working to gain power, developing business deals such as the Ocean House Hotel and holding a high-profile auction of valuable paintings of Caine at the Gallery Noir.
Ultimately it is revealed that Therese and Jeanette are one and the same: two personalities inside one scrambled Malkavian mind. Therese is the real person, and Jeanette is a split personality she created as a child to deal with the trauma of being regularly molested by her father; Jeanette was a highly sexualized pervert who was able to enjoy her father's "attention", while also sparing Therese from remembering any of these unfortunate incidents, though as a side effect, Therese became rather cold and averse to intimacy. One day, her father unexpectedly molested the girl when Therese was in control, and Jeanette didn't take over for some reason; the resulting trauma lead Therese to murder her father, subsequently spending time in a mental asylum, where she was Embraced by a fellow inmate who was actually a Malkavian vampire. The innate insanity of the Malkavian clan reinforced and solidified the two split personalities into complete, distinct entities with separate emotions and memories from each other, going so far as to have both of them believe that the other exists separately from herself, and is her twin sister.
When the truth comes out, Therese and Jeanette get into a surprisingly physical struggle over a handgun, each sister possessing the body in turn, explaining themselves to the player, who can encourage one "sister" or the other to overcome her other personality; if this happens, that personality will fire the gun in the air, metaphorically "killing" the other personality forever, and leaving the body to whichever one is left. However, if their conversational stats are high enough, the player can also persuade Jeanette and Therese to co-exist, now fully aware of their status as halves of the same whole. If this is done successfully, the resulting woman displays elements of both sister's personalities in the way she carries herself; she is referred to in the game files as "Tourette", an amalgam of Therese and Jeanette's names and an amusing reference to Tourette's Syndrome.
The player can sleep with Jeanette during later stages of the game if he or she is always nice to Jeanette and gives her the pendant from the Ocean House Hotel (note: doing this will cause the failure of the quest).
One of the hallmarks of the Malkavian Clan is their ability to see the future and perceive hidden secrets, with their insanity making it difficult for anyone else to make use of their information. Reflecting this, if the player character is Malkavian, his or her dialogue with Therese and Jeanette refers to the sisters as the Dark and Light Daughters of Janus. Janus is a Greek god, the guardian of Mt. Olympus, for whom the month January is named. To better protect the gate to the kingdom of the gods, Janus had a face on both sides of his head, allowing him a 360 degree view of the area around him. Referring to the sisters as "daughters of Janus", even before the big reveal, indicates that the player Malkavian is on some level aware of their existence as two "faces" on the same person.