Rich Sommer

Sherlock will soon get a little help from his friends!

Mad Men's Rich Sommer will reprise his role as Harlan Emple, one of Sherlock's "irregulars," on the upcoming third season of Elementary, TVGuide.com has learned exclusively.

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Harlan, who assisted Sherlock in Season 2 after a mathematician was murdered, will come back into Sherlock's world when he finds a dead body during a math-based puzzle hunt.

Sommer, whose credits also include CSI and Law & Order: SVU, will appear in an episode slated for November.

Elementary returns Thursday, Oct. 30 at 10/9c on CBS.

(Full disclosure: TVGuide.com is owned by CBS.)

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