The Heroes and Alias alum will play Len Bryant, a white-collar everyman fighting addiction at a high-end rehab facility. He is determined to get sober in order to win back his children. Grunberg's episode will air in early November.
CSI returns Sunday, Sept. 28 at 10/9c on CBS.
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Watch Jennie Garth and Tori Spelling rank their Beverly Hills, 90210 boyfriends in chronological order: