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David Krumholtz knows how to play a professor. After perfecting the role for six seasons on Numb3rs, he'll go back to the classroom for his upcoming guest spot on Law & Order: SVU. But Krumholtz says the two parts are very different.

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"It's certainly one of the more intense roles I've played in quite some time," he says about the character, who he calls a rabble-rousing firebrand. "A guy who's sort of on edge with a cause, fueled by love — I haven't really done much of that in my career."

On Wednesday's episode, a female murder victim poisoned by toxic mushrooms leads the team to Krumholtz' character, a crazed activist and professor. Executive producer Neal Baer says that Detective Benson, Stabler and Co.  connect the case to the professor through privatized water — the victim had led the campaign for it, while the professor railed against it. His indignant behavior also raises doubts and Krumholtz says, "they figure out that he is worth being suspicious of, but may not be the guy who actually did it."

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The guest role marks the 32-year-old's return to television since the cancelation of Numb3rs."There is a grief associated with the end of any series," he says. "It was very important that I jump back into something that gave me that feeling and passion, and reignited the flames for me again. And this role afforded me that opportunity."

Law & Order: SVU airs Wednesday at 9/8c on NBC.