This Christmas season is different. For one thing, Mildred's humans have two unexpected house guests. Cyndi, good friends with Mildred's owners Frank and Fergie, and her socially awkward cat, Mittens, can't stay at their home. Cyndi's dad has COVID. She wants to be home to help, but her parents don't want her to get sick.

Mildred has her hands full keeping an eye on Mittens, getting her own puppy, Goofball, to avoid eating bubbles, and making sure Cyndi doesn't do anything foolish. On Christmas Eve, Mildred awakes to suspicious noises. She needs to get her humans out of bed and on a mission to help a friend who doesn't seem to know what's best for her.