Mitch Larsen is Stan Larsen's wife, a girl from the wrong side of the tracks who found peace as a housewife and the mother of three children, Rosie, Denny, and Tom. Mitch raised Rosie to be more modest and accomplished than other girls her age, though after Rosie's death, both Stan and Mitch's sister, Terry Marek, wonder if Mitch's strict approach drove Rosie to live a secret life that led to her murder. Unbeknownst to most people, Rosie’s biological father is a man named David, whom Mitch met during a break in her relationship with Stan.
Rosie's death stuns Mitch into a grief so deep that one night she tries to recreate the experience of drowning, submerging herself in bath water for a long moment before bursting to the surface, gasping for air. Mitch spends hours in Rosie's room, staring at its contents. At one point convinced that Rosie's teacher, Bennet Ahmed, killed her daughter, Mitch influences Stan to administer justice himself. Stan drives Bennet to a secluded location and beats him so severely that he nearly dies. With Mitch overwhelmed by sadness, Terry takes charge of Denny and Tom. The one day that Mitch offers to help with the kids, Mitch becomes distracted and leaves them in the family's SUV in the garage with the motor running.
While Stan is in jail for the assault, Mitch learns that he has reconnected with Janek Kovarsky, a Polish mobster for whom Stan once provided muscle. Stan admits to Mitch that he went to Janek for a loan, but she cuts him off before he can reveal that the money was to help cover the mortgage on a house he'd recently bought to surprise her. Enraged, Mitch refuses to post Stan's bail. When he returns home after Terry posts his bail instead, Mitch tells him that the boys don't need her anymore. Stan replies that both he and the boys need her, but Mitch just sobs, "Everything about this place hurts me." That evening, she leaves her family.
While away from home, she checks into a motel and kisses a man that she meets at a bar. She also takes a teenage girl under her wing, but the girl ends up robbing her. Mitch finally returns home and, in a sign that she’s ready to move on from Rosie’s death, agrees with Stan’s suggestion to move to a new home.
Forbes currently stars in the AMC series The Killing. Her portrayal of a grief-stricken mother earned her an Emmy nomination for Outstanding Supporting Actress. Prior to that, Forbes starred in the groundbreaking Alan Ball series for HBO True Blood, as Maryann, a maenad who wreaked havoc in Bon Temps. Additionally, she starred as Kate Weston in the HBO series In Treatment, opposite Gabriel Byrne and Dianne Wiest. Forbes also starred in the award-winning Canadian series Durham County as Dr. Penelope Verrity, a forensic psychiatrist who is fighting her own psychological collapse, for which she won the International Monte Carlo Golden Nymph award for Best Actress.
In the 90s Forbes appeared in such independent films as Kalifornia, starring opposite Brad Pitt and David Duchovny; and Swimming with Sharks with Kevin Spacey, to name a few. In 1996, Forbes was asked to join the award-winning series Homicide: Life on the Street, having met Tom Fontana that same year when she starred opposite Stockard Channing in the television movie The Prosecutors, also written and produced by Lynda La Plante, the creator of Prime Suspect. Forbes then went on to do the critically hailed yet controversial and short lived series about a mental hospital Wonderland for ABC, as well as Johnson County War, an epic western filmed for the Hallmark channel. Terribly fond of working in the UK, her other series credits include a three year stint on the lauded BBC television series Messiah opposite Ken Stott, and a recurring role on the BBC1 drama Walking The Dead. She is also a veteran of the 2nd season of 24, playing Lynn Kresge.
In 2005, Forbes starred as Admiral Helena Cain in the intelligent and politically charged Battlestar Galactica. In addition to her extensive television work Forbes has continued to appear in such independent films as Dandelion, which was received admirably at Sundance.