Bernadette and Howard go to the hospital so she can have a sonogram. In the meantime, Lenny and Shamy have a dancing party together and Raj, Emily, Stuart and Alex are at the comic book store trying to start a new going-on for the shop.
Leonard, Penny, Sheldon and Amy decide they want to go dancing. They get dressed in smart and lovely outfits and later when they go out to the dance hall, they find that they can't get in because they find that the dance is only for teenagers. This upsets everyone, especially Sheldon, who was looking forward to dancing with his girlfriend. He comes up with a plan to disguise themselves as teenagers so they can get in. The others are not very fond of the idea, but seem to think better of it. They buy some teenage clothes, put them on in separate cubicles in public toilets and return to the dance hall. They enter the hall and start to party and dance, like crazy. But later, they lose their disguises when Sheldon's identity card falls out of his pocket and his date of birth is noticed by a male teenager. Security is called in and the guards try to catch Leonard, Penny, Sheldon and Amy. The 4 friends run for their lives, until they are far away. Leonard, Penny and Amy are mad at Sheldon for doing this and he feels sorry. He then tells them that during the run, he came up with an idea: They can do a dance party at the apartment and Leonard, Penny and Amy like that idea. Later, they are seen dancing together to soft romantic music with Penny and Amy cuddled up to their lovers and both couples exchange kisses.
Since Howard and Bernadette are having a baby, they go to the hospital so Bernadette can have a sonogram done. Bernadette's obstetrician starts the sonogram and while doing it, she finds that there are like three feet and two heads in there which causes Howard and Bernadette to get a little freaked out when they hear what the doctor is saying and they keep asking if they're having a peculiar baby, like maybe a baby alien and she tells them to calm down and not to be crazy and not to worry. She continues the sonogram and after finishing, she reveals that Bernadette is pregnant with twins! Howard and Bernadette are surprised since they were thinking that Bernadette was pregnant with only one baby. The doctor asks them if they want to know the genders of the babies and they do. The doctor tells them that they are a boy and girl, making Howard and Bernadette even more relieved.
At the comic book store, Raj, Emily, Stuart and Alex are busy discussing on how they could make the store a better place and so they can also have children visit. They suggest that the store should also sell comics for kids and also only-boy and only-girl magazines. They also suggest that there could be puppet shows and a TV for children to watch shows for their age. Stuart is happy with all the ideas and they plan to set up these new features.
In the final scene, all 10 members of the gang are at Howard and Bernadette's house and the other couples are amazed that the Howardette couple are having twins. Sheldon feels a bit scared because of the fact that he is a twin and that his twin sister used to torture him in his past and fears the twins will do the same to the other. Howard and Bernadette assure him that if they fight, they'll take care of it and that there are lots of people who can also help. Sheldon is calm again. The rest of the gang is shown the sonogram and they are all amazed at the babies' images. They all smile happily until suddenly the doorbell rings. Howard goes to answer it and when he opens the door, he says 'Dad?'.
TO BE CONTINUED...