Alexander's terrible day continues as he experiences a series of embarrassing mishaps at school, including failing a science experiment and being humiliated in front of his crush. Meanwhile, his family members also encounter their own misfortunes – his mom fails a job interview, his dad accidentally sets fire to his office, his brother gets sick during a school play, and his sister struggles with her driving test.
Feeling like the unluckiest person alive, Alexander makes a wish that his family could understand what he's going through. The next morning, they all wake up to find that they are experiencing their own series of calamities, just like Alexander did the day before.
As they navigate through their own terrible, horrible, no good, very bad day, they realize the importance of sticking together and supporting each other through tough times. By the end of the day, they come to appreciate the love and bond they share as a family, no matter what challenges they face.
In the end, Alexander learns that bad days happen to everyone, but having the love and support of his family makes it all bearable. The film is a heartwarming comedy about the ups and downs of life, and the power of family to get through even the toughest times.