The episode opens with Bernadette and Howard sitting in the back seat of their van, as Raj drives them to the hospital. As Bernadette has another contraction, Stuart (who's in the passenger seat) tells Raj to speed it up, so Raj starts yelling at passerbys as if he's in India.
Meanwhile, Sheldon wakes Amy up at midnight to wish her Happy Birthday. He gives her a framed MRI of his brain as a present...and then immediately puts the moves on Amy to get the "coitus" portion of her birthday out of the way. Unfortunately, their intimate time is interrupted by Penny and Sheldon informing them that Bernadette is having a baby.
At the hospital, the nurse sends Bernadette home as her contractions are too far apart. When Raj and Bernadette call Penny, Amy suggests to Sheldon that they resume their earlier activities. It takes Penny a minute to get the hint (she wanted to go to the bar to celebrate Amy's birthday), but a wheezing Leonard clues her in shortly before he declares he needs to find his backup inhaler.
Raj starts to record a video for the baby, but inadvertently spoils the sex of the baby (it's a girl). Both Bernadette and Howard are upset...especially when Stuart snitches that Raj told him the sex too.
Sheldon and Amy try to restart their evening activities, but Sheldon is having trouble as they're trying to force the moment. Amy suggests she put on something to put him back in the mood.
Meanwhile, Leonard and Penny also decide to have sex but they get interrupted by Raj, who was kicked out of Bernadette and Howard's place for spoiling the baby's sex.
Amy puts on a Harry Potter robe to spice things up and gives him a corresponding set of Gryffindor robes to match. Sheldon briefly gets upset that Amy went to Universal's Wizarding World park without him, but quickly starts things up again. Unfortunately, Raj interrupts....followed by Penny announcing that Bernadette's water broke.
Stuart takes Bernadette and Howard to the hospital (very slowly), while Penny drives the rest of the gang to the hospital. On the way there, we find out that Sheldon and Amy's last bout of sex lasted for hours, while Raj pouts that he's not there to share Bernadette and Howard's moment.
Howard and Bernadette start brainstorming names for their baby girl. Bernadette suggests naming the baby after Howard's mom, which leads to a fond remembrance of how she always had candy on hand.
The rest of the gang contemplates how far they've come over the last decade, but Raj throws a hissy fit about how he hasn't progressed much at all over the last 10 years. He tries to visit Bernadette and Howard, but Bernadette isn't having a great labor so he quietly sneaks away.
After a few hours of the gang unsuccessfully trying to cheer Raj up, Howard announces that they've had a baby girl named Halley (as in Halley's Comet). He also names Raj as Halley's godfather.
Later, the rest of the gang visits the nursery hoping to get a glance of Halley. They try to figure which one is Baby Wolowitz, but quickly figure it out based on a cry that sounds an awful lot like Howard's mom.
The episode ends with Amy and Sheldon returning from the Wizarding World of Harry Potter. Sheldon declares that it's time to finish Amy's birthday session with some sex and says that seeing a magical train AND reporting someone for cutting in line was the best foreplay of all.