This week on a brand new "The Big Bang Theory" season 9 steers towards the finish line with an episode titled, "The Line Substitution Solution." Penny and Sheldon play a game of flashcards at the start of the episode. His are elements and science related images, like helium, and hers are celebrities, like Taylor Swift, and each player has to guess the image displayed. Leonard walks in and plays along, Sheldon's image is a hydrogen atom and Penny's image is Adam of Maroon 5. He does an imaginary mic drop having getting both correct.

Beverly Hofstadter comes to visit

Leonard's mother,Beverly Hofstadter, played by Christine Baranski, is coming in to town and Lenoard and Penny talk about going to pick her up. Penny agrees to do the task alone and Leonard is relieved. At the comic book store, the guys talk about going to a special screening of "The Avengers" that night with a Q&A with director Joss Whedon. Sheldon is disappointed he can't go because he has to go shopping with Amy, but Howard talks about hiring someone to wait in line for him.

Sheldon takes the idea to the next level, but there are consequences for him later in the episode.

Penny and Beverly get reacquainted

Beverly Hofstadter asks Penny if Leonard has problems with erections and Penny asks if they can talk about books instead of her husband's sex organs. Penny then asks if Leonard's mom can stop psychoanalyzing everything she says. Beverly makes a joke about how that makes Penny feel and they eventually make plans for dinner that night with all the girls.

Meanwhile, Sheldon hires Stuart to go shopping with Amy and she's annoyed by the situation. Sheldon, now at the movie with Howard, Raj and Leonard, is talking with the guys about all the lines they've been in together when Stuart shows up. Stuart tells Sheldon he is inconsiderate and tells him Amy is bent out of shape and she's hired him to let Sheldon have it.

Beverly has dinner with the girls

Amy goes on and on explaining her relationship problems to Beverly, who says maybe her issue is Sheldon can't get in a word edgewise.

Beverly admits that Sheldon can be a bit to handle. Meanwhile, Penny wonders why she cant bond with Leonard's mother like Amy does. Stuart shows up to the dinner because now Sheldon has hired him to say he's sorry with flowers. Amy pays $5 to Bernadette to slam the door on him.

Sheldon apologizes in person to Amy

When Sheldon's proxy apology to Amy fails, he hires Stuart to stand in line for him so he can go apologize in person. Meanwhile, the girls are still having dinner at Penny's house, but she's finding it hard to get in the conversation. Sheldon shows up and has a three part apology, which Amy accepts reluctantly.

Sheldon quickly gets back to the movie theater where he sees a person skip in line ahead of him. Sheldon takes it upon himself to call out the offender. It ends badly with Sheldon bringing up Rosa Parks, but no one else cares about the line skipper. Sheldon is then called out by another person behind him in line for skipping, but Sheldon explains his action was a swap and not a skip, because he paid someone to stand for him and they left. Sheldon reluctantly lets it go as the guys go inside to see "The Avengers" special screening.

The wedding redo

Beverly asks Amy and Bernadette if they want to be interviewed for her new book about relationships.

Bernadette asks Beverly about Penny being interviewed and it turns into an argument between mother-in-law and daughter-in-law. Beverly is still upset and insulted about not getting invited to their wedding. Penny apologizes and Beverly admits she wouldn't have gone to the wedding but rather told them they were making a mistake. However, Beverly admits she's never seen her son as happy as he is now, so maybe she was wrong. Penny asks if a wedding do over with Beverly present would make things right, and she agrees. Next week we meet Leonard's father in the season 9 finale in an episode called, "The Convergence Convergence."

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