Penny buys Leonard and Sheldon “Star Trek” collectibles as a thank-you, leading Sheldon to be haunted by Mr. Spock. “Star Trek” legend Leonard Nimoy voices Mr. Spock.

On Friday, upcoming Big Bang Theory guest star Leonard Nimoy tweeted a geektastic image from the set of the CBS sitcom.

The Star Trek legend is set to be heard, not seen in next Thursday’s episode when he speaks to super-fan Sheldon, as Spock, in a dream sequence.

“We’ve been chasing Leonard for years, and he finally gave up,” Big Bang cocreator Chuck Lorre recently told TVLine. “We caught him.