Mare Winningham Mare Winningham

Get ready to meet more residents of Chester's Mill!

Mare Winningham has been tapped to guest-star on Under the Dome, has learned.

Winningham will play Agatha, a seemingly warm woman acting as a caretaker for a house. She'll even welcome Big Jim (Dean Norris) into the home, but we'll learn that her intentions are anything but sincere as we discover her ties to the town.

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"I'm thrilled to be working with Mare Winningham on Under the Dome," said executive producer Neal Baer. "She's my good-luck charm: I worked with her on ER, as well as on Law & Order: SVU (for which she was Emmy-nominated as Best Guest Actress).  She brings truth and believability to every role and she will definitely leave viewers talking."

The Emmy-winning and Oscar-nominated actress, who is well known for her roles in St. Elmo's Fire, Georgia and Hatfields & McCoys, will appear in at least one episode slated for late August.

Under the Dome airs Mondays at 10/9c on CBS.

(Full disclosure: is owned by CBS.)