Nicole Richie will battle secretive operative Sarah (Yvonne Strahovski) in a shower, Chuck creator and producer Josh Schwartz reveals.

Nicole Richie will battle Yvonne Strahovski in a shower

"The premise of the episode is Sarah has to go back to her high school reunion where she was not so popular and not nearly as beautiful," he tells OK! at a TCA conference.

But the reunion is not all fun and games. Sarah and Chuck (Zachary Levi) are there on a mission -- tailing Nicole's character, a mean girl who "tortured" Sarah back in the day.

"While there, things go awry," Josh teases. "The old high school shower becomes the location of a seriously wet showdown."

"Nicole came guns blazing," Zach tells OK!. "She was ready, she was prepared, and she had a good time."

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