Get ready for the mother of all CSI episodes, because we’re about to meet Gil Grissom’s long lost mother! EW has learned exclusively that Tony award-winning actress Phyllis Frelich will play the role of Mrs. Grissom – and go head-to-head with the new Mrs. Grissom – in an episode tentatively scheduled to air Feb. 3.

Here are the details: A murder occurs at a school for the deaf where Grissom’s mom is a professor. Sara (Jorja Fox) goes to investigate but ends up facing an unexpected challenge – a surprising lack of affection from her mother-in-law. Apparently, Grissom’s mom never felt that Sara was the one for her beloved Gil so the two women have a few fences to mend. The episode also stars Oscar winner Marlee Matlin as a school colleague who not only serves as Mrs. Grissom’s protege but used to date Gil. Guess who momma Grissom prefers?

Sadly, William Petersen won’t appear in the episode. (Fans are supposed to think that Gil is contantly on the move so he and Sara maintain a long-distance relationship.) But the story is a continuation of an arc that started way back in season one’s memorable …Sound of Silence" episode, in which we first learn that our hero can sign because he grew up with a deaf mother.

Frelich, who is deaf, won a Tony Award for her work in the 1980 Broadway production of Children of a Lesser God – the play that inspired the movie of the same name that starred Matlin, who won an Oscar for her role. Frelich has also appeared in numerous TV shows, including ER, Diagnosis: Murder and L.A. Law.