The gang brought things back to the past on “The Big Bang Theory” as the boys tried to track down some of the Bitcoins they mined seven years ago. However, looking back can sometimes do more harm than good, as they learned in Season 11, Episode nine.
The episode opens with the boys going into the comic book shop discussing the surprisingly high value of a single Bitcoin in 2017. They remember that, in 2010, the thought it’d be fun to spend the night coding and mining them online. They’re not sure how many they had, but at roughly $5,000 a pop, they’re eager to find out.
However, when Stuart tries to fix his money problems by pretending he was in on the mining, the boys were forced to remember what really happened. In a flashback to seven years ago, they discover that, although they offered Stuart a chance to help, he declined. Additionally, they forbid Sheldon from helping when he got too excited about the tax implications of mining Bitcoins.
Later that day, Raj and Leonard are at Howards as he digs out his laptop from 2010. They search everywhere for the Bitcoin they downloaded, but come up short. Howard flashes back to seven years ago and remembers that his mom distracted them while he was trying to figure out why his laptop kept crashing. They realize that they actually downloaded the Bitcoin on Leonard’s computer.
They go to his apartment but can’t find it either. Sheldon is there with Amy and revels in the fact that he remembers what happened and they don’t. He eventually tells them, after another flashback to Penny's time as a waitress, that Leonard gave it to Penny early in their relationship in order to bribe her to stay with him. However, she reveals that she gave the laptop away to her ex-boyfriend during one of her and Leonard's many breakups.
Leonard is mad, but he softens when Penny’s ex reveals all the sweet things about him he found on her old computer.
At last, the search for the Bitcoin appears over as they rush the laptop back home to Raj and Howard. However, predictably-enough, they aren’t on the laptop. That’s when a smug Sheldon reveals his master plan that’s been in the works for years. He snuck onto Leonard’s laptop, downloaded the Bitcoin onto a flashdrive and hid it in plain sight. He cherishes the moment when he can tell Leonard that it’s been on his Batman keychain the whole time.
“Sheldon, I lost that keychain years ago…”
Just like that, the boys were out their significant sum of money. However, the mystery was solved in one final flashback. Four years in the past, Stuart is sweeping the comic book shop when he comes across a batman flashdrive on the floor. He muses that he could probably delete it and sell it for about $10.