Why would someone need to procure such a large amount of helium that he has to turn to the black market? Science, people. Science. That’s the reason Sheldon and Leonard make the acquaintance of a shady chemical dealer played by guest star Michael Rapaport in an upcoming episode of The Big Bang Theory.



In Oct. 26’s “The Helium Insufficiency,” a worldwide shortage of helium poses a big problem for the fellas when they require a generous supply to complete an experiment. With no other means to get their hands on the goods, “they turn to a sketchy black market chemical dealer played by Michael Rapaport to score what they need,” according to CBS’ storyline description.

The Emmy-winning series, now in its ninth season, has focused much of the new season on the love lives of Sheldon (Jim Parsons) and Leonard (Johnny Galecki). Mr. Cooper was dumped by girlfriend Amy (Mayim Bialik) in the Season 8 finale, just as he was about to propose to her, and he hasn’t yet had much luck wooing her back.

As for Leonard, eight seasons of on-again, off-again romance with neighbor Penny (Kaley Cuoco) not only culminated in their marriage in the Season 9 premiere, but finally gave Penny a last name: Penny Hofstadter. The newlyweds will take another big step forward in Oct. 12’s “The 2003 Approximation,” when Leonard finally moves in with Penny and Sheldon goes looking for a new roommate.

Rapaport, meanwhile, has a full-time gig on TNT’s Public Morals, in which he plays Charlie Bullman, the NYPD partner of Terry Muldoon (Ed Burns).

The Big Bang Theory airs Mondays at 8 p.m. on CBS.