Ms. Vivian McCarthy is an anti-hero in MOUSE: P.I. For Hire. She is an actress in Mouseburg and one of Jack Pepper's customers as well as the best friend of the late Betty Lynch. She is voiced by Rhiannon Moushall.

Despite being immoral and ruthless in pursuing her career, she is willing to fight for the justice of her friend.

A fame-seeking actress, Vivian has no qualm doing shady stuffs to get ahead including spiking a director's drink with blue cheese to blackmail him to get her a lead role. Eventually she befriended a fellow aspiring actress Betty Lynch who is as equally cutthroat as her. After Lynch was murdered for sticking her nose where she does not belong, Vivian swore revenge for her death.

She approaches Jack to investigate the death of her dear friend Betty Lynch with a promised of handsome payday. According to her, Betty Lynch's death was not an accident but actually a murder and she suspected the higher-up in Tinsel Bros are responsible due to her and Lynch's past blackmailing toward their high-up to get a lead in their career. However, she eventually discovered that BMP is behind Lynch's death.

Later on, she orchestrates the death of Miles Curd by supplying the drug-addict high-wire artist Francesco with high-grade blue cheese to cause him to fall on top of Curd to flatten him to dead. Jack's investigation eventually leads him to a ledger and letter from a mob bookkeeper that expose her crime. Cornered, she escapes Jack to her studio to pack up and leave the country for good.

Jack chases her and is forced to fight her bodyguard. However, she manages to escape in the end and reveals the true culprit behind Betty Lynch's death.