First, we see Alex being diapered for the night before bedtime. She lies down and is powdered and taped into a white diaper before bedtime. She's deeply embarrassed by needing to wear diapers, but can't stop herself from slipping into sounding childish about it.
The next morning, we see Alex coming out to see her Daddy and talk about the day...in a soaking wet diaper. She is reminded that this is why she has to wear diapers despite her age. Daddy suggests that Alex should wear a pullup when they go out that day, but Alex begs him not to make her. So, instead, he changes her out of her wet diaper and puts her into a pair of panties with a "pee pee pad". But once he leaves to give her privacy as she finishes dressing, Alex takes the pad out since she hates wearing it. It's just too embarrassing.
In the final part of the film, we see Alex and her Daddy coming home. Alex's shorts are soaking wet: she had an accident at the mall and wet herself. Since there was no pee pee pad to soak things up and she insisted on no pull-ups, she's very wet indeed. She is in big trouble, though: she was told to wear the pad and took it out. So, Alex is sent to get her hairbrush and then is put over Daddy's knee for a spanking, first on her soaking wet, high cut, vintage style panties, then on her bare bottom. The spanking hurts and when she is punished with the hairbrush, Alex starts to cry real tears from both pain and embarrassment.
When Daddy is convinced that she's learned a lesson, Alex is sent to her room to go get ready to be put in a fresh diaper for the rest of the day.