Sheldon Cooper (Jim Parsons) has long been a closed book in the television series "The Big Bang Theory," but the upcoming episode will unveil more about TV's favorite quirky nerd genius.

In season 11, episode five of the long-running situational comedy (sitcom), it is revealed that Penny (Kaley Cuoco) may have found an answer to Sheldon's mystery in the form of a book. The "Big Bang Theory" promo for the upcoming episode showed that Penny has confidently claimed that she has found the "answer key to the Sheldon test."

The episode, titled "The Collaboration Contamination," will revolve around the said book, as it may contain sensitive information on how Sheldon thinks. Penny also hints that she may have found a way to control Sheldon using the book. Her husband Leonard (Johnny Galecki), however, was in disbelief, even going so far as to ask Penny if she dabbled in witchcraft just to get back at Sheldon.

The promo trailer also shows Sheldon behaving in a seemingly "normal" manner, in contrast to his eccentric self. He is shown inviting his fiancée, Amy Fowler (Mayim Bialik), to sit down to be "pampered." This is something new for fans since Sheldon was usually cold and indifferent to her. In addition to that, Sheldon is also seen doing household chores in the next episode, and in good faith too, something not natural to his character

It would seem that Penny has really discovered Sheldon's kryptonite this time, though how long it will work remains to be seen. It is not yet known what the book will contain, but it looks like it will be the most effective tool to unlock the mystery that is Sheldon.

Fans will find out more about the book that can be used to manipulate Sheldon once episode five, "The Collaboration Contamination," airs later today at 8 p.m. EDT on CBS.