Joan Allen — best known for playing heroines in The Contender, The Crucible and Face/Off — jumped at the chance to go bad in the TNT miniseries The Mists of Avalon (which concludes tonight at 8 pm/ET).

"It really appealed to me when I found out they offered me the role [of Morgause]," the 44-year-old three-time Oscar nominee tells TV Guide Online. "My agent said, 'It's a villain,' and I said, 'Send me the script! Send me the script!'"

In the two-part epic, which is based on Marion Zimmer Bradley's retelling of the Arthurian legend, Morgause lies and schemes her way to power. Co-star Anjelica Huston — Morgause's rival and sister, Viviane — was taken aback by Allen's dark turn. "Let me tell you, when she's flying down the stairs at you with a dagger in her hand, it's daunting," she recalls of Mists's climactic scene. "I think she was really superb in this — and gleeful. You could tell how much fun she was having with it."