Big Bang Theory season 11
Penny and Leonard in The Big Bang Theory series CBS

The Big Bang Theory season 11 has taken a week-long break (for the Thanksgiving weekend) and will return with fresh episodes on 30 November at 8 pm EST on CBS Network.

CBS has released the official synopsis and promo for episode 9, which teases a big secret for Penny and Leonard. A leaked plot description hints at the return of Penny's old boyfriend. [Spoilers ahead]

Episode 9 is titled, The Bitcoin Entanglement and the official synopsis reads as follows:

Sheldon tries to teach the guys a lesson after they cut him out of a potentially valuable Bitcoin investment. Also, a seven-year-old video reveals a secret about Leonard and Penny's relationship.

In the episode, the gang flashes back to 2010 as Leonard tries to remember where he kept a potentially valuable investment. The chapter will reportedly be dedicated to Bitcoin, a digital currency.

According to a leaked report in a fan page, the chapter will feature the return of actor Brian Thomas Smith as Zack aka Penny's old boyfriend. "The guys find a laptop which has some virtual Bitcoin currency on it. The computer belongs to Penny's old boyfriend Zack," said the leaked report.

Big Bang Theory season 10 episode 22
Penny's ex-Jack returns in The Big Bang Theory season 10 episode 22 CBS

Zack was last seen in season 10 episode 22 titled, The Cognition Regeneration, where he offered Penny a job, but Leonard was less than thrilled about it.

The report also has a photo attached, wherein we see Leonard, Penny and Zack staring at something on the computer, possibly teasing the seven-year-old secret about the Hofstadter's relationship.

The Network has also a promo for the episode, which opens with the gang in Stuart's Comic-Book store talking about Bitcoin investment. Howard says, " Can't believe that a single Bitcoin is $5,000."

Later Leonard asks Rajesh what he will do with his share of the money. "I will buy a big tiger," Raj replies. However, the voiceover warns, " Don't count your Bitcoin before its..." as we see the guy excitedly checking their laptop.

Leonard asks, "How much is in there?" to which a baffled Howard says, "Its empty."

Then we see Sheldon being smug, as Leonard asks, "You know where it is?" Sheldon, who has a photographic memory, asks Amy, "Should I be the bigger man?," to which she tells him, "You should."

However, Sheldon is bent on teaching his friends a lesson and shrugs off Amy's opinions, saying, "Why did I ask you?" Looks like the upcoming episode is worth the wait.