Sheldon (Jim Parsons) and Leonard (Johnny Galecki) will once again be at loggerheads with each other in the upcoming episode of "The Big Bang Theory."

It appears that Leonard is still angry at his best friend for divulging a secret he has been keeping from Penny. Last episode, the newlyweds went on a cabin trip with Sheldon and Amy (Mayim Bialik). Unfortunately, a rainstorm marred what could have been a fun outing. The couples were forced to stay inside and play drinking games instead.

A drunk Sheldon suddenly revealed that Leonard was keeping a secret bank account because he believed Penny's credit card debt was too much. Penny was of course very surprised to hear that, but Leonard managed to smooth out everything with her. She told him that perhaps she really needed a change of career. Although things worked out all right with his wife, Leonard may still be feeling raw about what happened.

In the upcoming episode titled "The Viewing Party Combustion," CarterMatt reports that Leonard will lose his temper with Sheldon during the group get-together to watch a television series premiere. While, at first, their friends will think it is going to be one of their petty quarrels, the argument will soon get out of hand and Penny, Amy, Howard (Simon Helberg), Raj (Kunal Nayyar) and Bernadette (Melissa Rauch) will be forced to take sides on the fight.

Leonard and Sheldon have been friends for a long time. They have had each other's back for years and even shared an apartment until Leonard married Penny. Sheldon always claims that the marriage ruined things for them. On the other hand, Leonard has always been the one who defends Sheldon to their other friends whenever the latter is in one of his moods. Will they be able to patch things up soon?

"The Big Bang Theory" season 9 episode 21 airs Thursday, April 21 at 8 p.m. EDT on CBS.