If I had to predict the topic that would make for the best episode of The Big Bang Theory since Sheldon and Amy had sex for the first time, bitcoin would have been super low on the list, even if that list were alphabetical. Yet “The Bitcoin Entanglement†employs a sitcom cliché — the flashback episode — to not only tell a funny story about Sheldon and the gang, but to also give the most uncomplicated explanation of how bitcoin works I’ve ever heard.
The story begins at Stuart’s comic book shop, where Sheldon, Leonard, Raj, and Howard remember a time seven years earlier when they mined bitcoin. That kicks off a search to find the cryptocurrency, which, the guys say, is valued at $5,000 each.  Unfortunately for Leonard, Raj, and Howard, Sheldon and his eidetic memory could put this forgotten bounty in their hands tout de suite, if only they hadn’t kicked him off the mining project seven years earlier because he was being so Sheldon-y.
Flashback: Everyone looks the same, is wearing the same kind of clothing, and even Stuart’s comic book store isn’t so different, highlighting one of the most clever aspects of the episode. While most sitcom flashback installments are all about showing the viewer how the characters have evolved — Friends’ “The One With the Prom Video,†for example — the gist of this story is that TBBT’s core group of friends remains the same. (Save the fact that Penny and Bernadette were then Cheesecake Factory waitresses, and Amy was photographing her five-minute dates to keep her mother happy believing she had a social life. The women have evolved, which we TBBT devoted constantly note.)
As Sheldon explains to his friends, bitcoin is an online currency, there’s a limited amount of it, and they can get some for themselves by “mining†it, or writing code to solve complicated math problems. Add snacks, and that sounds like the makings of a party for this gang, until Sheldon warns them that there could be major tax implications and gets goosebumps when he imagines the time he’ll have to — get to — spend on the phone with the IRS. Leonard, Raj, and Howard decide to tackle the project without Sheldon.
Back to the present: That’s when Sheldon reminds the guys he told them someday they would regret their choice to proceed without him. “And do you know what today is?†he asks.
“The day we found out we’re rich, and none of it is yours?†Leonard asks, while slapping high fives with Raj and Howard.
Not quite, of course. A quick trip home to find the bitcoin on the laptop Howard was using in 2017 unearths nothing but his stash of pornography. In flashback — which provides an excuse for an appearance by the late mama Wolowitz — it’s revealed the guys didn’t use Howard’s laptop for the bitcoins. It was infected with a virus because of all the, ahem, music Howard was downloading, so Leonard volunteered his laptop instead.
Back to the present: Leonard, Raj, and Howard frantically search the living room closet in the Hofstadter abode for his 2010 laptop, only to come up empty-handed. Smug Sheldon sits nearby, taunting that he knows what happened to the laptop, and yes, he is still holding a grudge for being left out of the bitcoin adventure (which, to be fair, only commenced after he told his friends what bitcoin is). Will he be the bigger man and reveal to his friends the location of their fortune?
Flashback: Dinner at the Cheesecake Factory reminds us that Raj couldn’t talk in front of women, including Penny, at that time, and that Penny frequently messed up Sheldon’s order. Her acting career also wasn’t going so well. On this day, she missed an important audition, because her broken laptop left her with no access to an email notice. Leonard offers to let her use his.
Back to the present: Yes, Penny confirms, Leonard gave her his old laptop, the one that contains the bitcoin the guys mined … the same laptop Penny gave to her then-new, now-ex-boyfriend Zack during one of the many pre-marriage Lenny breakups. Penny calls Zack, who reveals he still has the laptop, and after some really tired jokes about Penny’s past promiscuity (sorry, but it’s never gonna be a five-star episode with those kind of jokes) she and Leonard visit Zack and get the laptop back. There’s even a flashback on the laptop itself, as a video shows a drunken Penny professing her love for Leonard before she passes out and falls off her chair.
At home, Leonard hands off the laptop to Howard, who quickly locates the bitcoin folder. He opens it to find they are the owners of bitcoin in the amount of … nothing. The folder is empty. Did Zack steal it, Howard wonders?
“He doesn’t know how to steal bitcoin,†Penny says about her dimwitted former lover. “He waves at trucks.â€
“Hmmm, who could it have been?†Sheldon wonders loudly, before telling Amy he plotted his revenge, and if she gets a dish, he’ll serve her some, cold.
He downloaded the bitcoin onto a flash drive, he announces, and at long last, he gets to tell them. Even better, the flash drive he used is the Batman flash drive Leonard keeps on his keychain, which — aha! — means the moolah has been in Leonard’s pocket lo these many years!
Except, it hasn’t. Leonard lost the Batman keychain years ago.
“I guess we’ve all learned a lesson today,†Sheldon says, but he doesn’t know what that lesson is.
Flashback to four years ago: Stuart is sweeping up after closing the comic book shop one night, and he finds a Batman flash drive. He thinks he’s hit the jackpot, because if he erases the drive, he can resell it, for $10.
“Things are finally going my way!†Stuart says.
THEOR-EMS
• The fellas should really, really, really be kicking themselves — and literally Sheldon — because the value of bitcoin just soared to $10,000.
• Stuart: “I’m having a special today: Buy something, keep having a comic book store to come to.â€
• Flashback Stuart, when Sheldon asks him if he’ll be accepting bitcoin: “Well, I don’t know what that is, but it’s got ‘coin’ in it, and my cash register doesn’t, so, yeah.â€
• Shamy gives Penny a quick update on their wedding planning. They were thinking about having the ceremony on a cliff overlooking the beach, but Sheldon didn’t like any of the locations. “Some were too beachy, some were too cliffy …†Amy says. “And all of them were too outside-y,†Sheldon adds.
• When Leonard doubts Sheldon could be holding a bitcoin grudge for seven years, Sheldon points out he has a grudge that goes back to preschool. “Someday I’m going to find a grown-up Elaine Dwyer and eat her favorite crayon while she watched,†he says. (Amy: “Is that why there’s an Elaine Dwyer on our guest list?†Sheldon: “Yes. That night, I’m going to have the first dance and the last laugh.â€)
• It was nice to see Penny’s ex, Zack — a dense, kind dude who’s made several guest appearances — until the writers felt the need to blow up the character’s vibe by mentioning his stalker-y obsession with his female neighbor, whose shower time Zack notes and shares. Also not five-star material.