Dennis Kim returns and upsets Sheldon again due to their earlier encounter years back.
Leonard, Sheldon, Howard and Raj are at work in the cafeteria eating. Dr. Eric Gablehauser, the head of the Physics Department comes over to their table along with someone. It is Dennis Kim, the once-child prodigy who came to Caltech 8 years before and had been an intellectual threat to Sheldon when surpassing him in every way. Eric Gablehauser is happy to have him back. He is now 23 years old and has gotten a job in physics at Caltech and is sharing an office with Barry Kripke. They both leave and Sheldon is once again threatened by Dennis's presence. Leonard, Howard and Raj say not to again do what they did to get rid of Dennis.
Later at Apartment 4A, the whole gang is together eating dinner and Sheldon brings up again Dennis Kim which drives Leonard, Howard and Raj mad again. Bernadette tells him not to let the guy get to him because people can't always be smart at everything and Stuart also says that it's not nice to tell people that you're better than them because it makes them feel bad inside. Everyone agrees with Stuart's words but Sheldon is too bummed. He gets up and goes to his room, leaving the other nine in the living room. Alex asks what they're going to do, but no one knows. Penny secretly suggests with Bernadette and Amy that they call Sheldon's mother Mary to come to Pasadena to help.
Later, Penny, Bernadette and Amy call Mary and they tell her what's going on. She is not pleased by this, so she offers to come to Pasadena to help. She arrives at Apartment 4B where the girls told her to come and greets the 3 girls by saying 'Hello' and kissing and hugging them. The rest of the gang is busy and occupied in other places, so Mary spends her time with Penny, Bernadette and Amy. They go shopping, have refreshments in a café, go to a spa for massages and see a movie at 4B when they return from their outing. That night, when the whole gang gathers in 4A for dinner, the guys, Emily and Alex wonder where Penny, Bernadette and Amy are and soon the girls come in with Mary. Sheldon is stunned to see his mother while Leonard, Howard, Raj, Stuart, Emily and Alex are overjoyed to see her and they all hug her one at a time. Mary turns over to Sheldon and hugs him and then later she and the others talk to him about how it's not nice to tell people that you're better than them, because it makes them feel bad inside and that they might try to fight fire with fire. Sheldon somehow now comes to terms a little bit of not being better than others and accepts that it's not nice to hurt people.
At the university, President Siebert announces that there is a Physics competition in 2 weeks and Dennis Kim is invited to participate and he needs someone to compete against. Sheldon says he wants to and President Siebert, Dr. Gablehauser and Dennis Kim accept.
In order to try and prepare for the competition, Leonard, Howard and Raj help Sheldon through all sorts of physics, even including computers, with some help from Bernadette, due to her finding Physics fascinating.
On the day of the competition, Mary and the other 9 members of the gang attend the Physics Competition. Sheldon and Dennis are seated and asked questions by Dr. Gablehauser. The contest goes on and on the final question: Dennis is ahead of Sheldon: 1360 to 1320. The final question consists of a physics equation on two separate screens which Sheldon and Dennis must try and solve and the one who answers correctly gets 500 points. Sheldon takes some time and tries to remember everything from what he and his friends looked at together and now, he seems to remember. He gives an answer and Dr. Gablehauser responds that "it's... correct!". Sheldon wins the competition and his mother and the whole gang cheer for him.
Later at 4A, Mary and the gang are celebrating Sheldon's victory and Sheldon apologizes to everyone for how he acted and has now come to terms that telling people that you're better than them makes them feel bad inside.