Grumpy Cat is a lonely cat living in a mall pet shop. Because she never gets chosen by customers, she develops a sour outlook on life...until one day during the holidays, a very special 12-year-old girl named Chyrstal (Megan Charpentier) enters the pet store and falls in love with her after realizing she is the only person who can hear this unique cat talk.
As the two develop a close friendship during the holiday rush, Grumpy reluctantly thwarts the kidnapping of an exotic dog she dislikes and on Christmas Eve, she rescues Chyrstal after the mall closes. Through her adventures, will Grumpy learn the true meaning of Christmas? Or will it be, in her words, the "Worst. Christmas. Ever?"
- Grumpy Cat as herself
- Aubrey Plaza as the voice of Grumpy Cat
- Megan Charpentier as Chrystal
- Daniel Roebuck as George
- Russell Peters as Santa
- David Lewis as Marcus Crabtree
- Evan Todd as Zack
- Isaac Haig as Donny
- Shauna Johannesen as Tabby
- Casey Manderson as Jesse
- Tyler Johnston as Gill Brockman