Baker Bob is bludgeoned to death with his own rolling pin by an unseen assailant he recognizes while baking a cake; he is the latest of twelve bakers to be killed. Meanwhile, Wallace and Gromit are running a "Dough to Door" delivery service from their bakery "Top Bun". On one such delivery, the duo save Piella Bakewell, a former pin-up girl mascot for the Bake-O-Lite bread company, and her miniature poodle, Fluffles, when the brakes on her bike appear to fail. They drive alongside so Wallace can attempt to use pastries to stop, but they careen into a zoo and barely escape being eaten by a crocodile. Gromit tests the bicycle brakes and becomes suspicious on learning that the brakes work perfectly fine, but Wallace becomes smitten with Piella.
A whirlwind romance ensues, during which it is also shown that the nervous Fluffles is treated rather shabbily by Piella. During the romance, Piella gives the entire house a "woman’s touch," decorating the whole house with dog romance pictures and flowers (including Gromit’s room). In addition, she pushes Gromit out of his relationship with Wallace and spends more and more time with him. Angry that Piella has interrupted his relationship with Wallace and modified the house, Gromit is about to start destroying the decorations when Fluffles stops by his room. Fluffles and Gromit share a sensitive moment after she timidly returns Gromit’s possessions, which have been discarded by Piella. However, when Piella leaves her purse at the house, Wallace decides to return it, but it is raining outside. Not wanting to get wet, he insists that Gromit return it instead. Upon arriving at Piella’s affluent mansion, Gromit discovers several dressmaker’s dummies in her bedroom, each wearing a baker’s hat and apron. In a book, Gromit discovers photographs of Piella with the murdered bakers. To his horror, Gromit discovers Piella is the "Cereal Killer" as he discovers a picture with Wallace as her apparent intended thirteenth victim, thus completing a "baker’s dozen." Gromit accidentally knocks over all the dummies, but gets them all back up again before Piella enters the bedroom, escaping detection by hanging from the chandelier. Despite Piella’s lavish ways, Fluffles has to sleep in an old cardboard box, covered with a tattered rag, implying years of mistreatment…
