The story takes place some time after One Hundred and One Dalmatians, where the pups are playing a game called Cruella de Vil, telling multiple tales on defeating Cruella. When Missy asks what she did in the tale, the other pups comment that she just sat in the back, since she isn't really a noisy pup. She tries to prove them wrong by barking, but no matter what she does, she can't make a noise.
Sgt. Tibbs then arrives, to the pups' delight, commenting on how he can't really bark, but he's okay as he is. Missy then sparks the idea that maybe she should start acting like a cat.
She asks Tibbs on this and, although surprised, agrees to teach her. First lesson was that cats need to keep themselves clean, but when she tries cleaning her tail, she begins to chase it. Next, she is playing with yarn; however, the yarn begins to unwind and soon both Missy and Tibbs are wrapped in it. Tibbs then tries rubbing against the Radcliffes' legs and when Missy tries it, the humans ridicule her cat-like behavior. When Roger begins dancing with Anita, Missy tries to rub against them again. She isn't as graceful and trips herself, Roger and Anita up.
When Roger takes her outside, Missy is upset that she can't be a cat, but Tibbs assures she tried her best. Missy then notices a van outside the house and then notices Horace and Jasper Badun approaching, ready to kidnap the puppies again. Missy tries to get in, but the door is closed and no one can hear her tapping on the window. Missy then feels something coming from within her, and she suddenly starts barking. Jasper tries to catch her, but she scampers away and keeps barking. Eventually, Roger hears Missy and comes outside, causing the Baduns to retreat.
After that, Missy is still quiet and thoughtful, but all the other pups wish to play with her now. Missy herself is happy for being a Dalmatian.
- Missy also appears in the book Rolly's Special Spots, claiming she has a spot in the shape of one of Roger's slippers. Her appearance shows her to have two white ears instead of one, and without a spot on her muzzle. Whether or not this is the same Missy may be up for discussion.