Meanwhile, Sheldon (Iain Armitage) is still dealing with the fallout from his trip to Germany and his complicated relationship with his university professor, Dr. John Sturgis (Wallace Shawn). The "Red-Sweatered Avenger" in the title refers to Sheldon's attempt to solve a minor injustice at home by adopting a vigilante-like persona—humorously channeling his logical mind into a secret mission.
This episode is the 18th installment of the fourth season of Young Sheldon , the popular prequel spin-off of The Big Bang Theory . It originally aired on CBS on April 29, 2021 . young sheldon s04e18 720p web-dl