The teammates crew create a invitations letter delivery, but when Jones falls in love with Isabella fairchild and naomy is jealous of her, Darlyn is left alone to solve a murder mystery.
The victim named Andrew ashworth is falls out of the ship to death with his own hammer by an unseen female assailant he recognizes while paking his things; he is the latest of eleven victim to be killed. Meanwhile, The teammates crew are running a "New years" letter delivery service from their friends On one such delivery, jones save Isabelle fairchild, a young woman mascot for the Grimsborough anniversary company, and her miniature mentee, Sarah miles, when the brakes on her bike appear to fail. They drive alongside so Jones can attempt to use pastries to stop, but they careen into a zoo and barely escape being eaten by a crocodile. Darlyn tests the bicycle brakes and becomes suspicious on learning that the brakes work perfectly fine, but Jones becomes smitten with Isabella.
A whirlwind romance ensues, during which it is also shown that the nervous Sarah is treated rather shabbily by Isabella. During the romance, Isabella gives the entire house a "party's touch," decorating the whole house with child romance pictures and flowers (including Darlyn's study room). In addition, she pushes Darlyn out of her relationship with Jones and spends more and more time with her. Angry that Isabella has interrupted her relationship with Jones and modified the house, Darlyn is about to start destroying the decorations when Sarah (who become a friend of Darlyn) stops by her room. Sarah and Darlyn share a sensitive moment after she timidly returns Darlyn's possessions, which have been discarded by Isabella. However, when Isabella leaves her purse at the house, Jones decides to return it, but it is raining outside. Not wanting to get wet, he insists that Darlyn return it instead. Upon arriving at Isabella's affluent mansion, Darlyn discovers several dressmaker's dummies in her bedroom, each wearing a police and agent's uniform, hat and badge. In a book, Darlyn discovers photographs of Isabella with the murdered victims. To her horror, Darlyn discovers Isabella is the "Serial Killer" as she discovers a picture with Her mentor, david jones as her apparent intended twelfth victim, thus completing a "victim's dozen." Darlyn accidentally knocks over all the dummies, but gets them all back up again before Isabella enters the bedroom, escaping detection by hanging from the chandelier. Despite Isabella's lavish ways, Sarah has to sleep in an tent, covered with a tattered rag, implying years of mistreatment.
Despite Jones being oblivious, Darlyn attempts to thwart Isabella by installing an airport-style metal detector in their home. After tricking Jones into thinking that darlyn bit her, Isabella almost succeeds at pushing Jones to his death whilst a chained up Darlyn can only watch, but she is thwarted by being struck by a bag of gravel from Her mixing contraption. After an angry outburst against agent, she leaves but returns a day later to apologise with a large cake. Jones says that it will do nicely for four o'clock tea. When Isabella is leaving to attend to the absent Sarah (who is "not well"), she tells her she will be getting a surprise. A worried Darlyn follows her home only to be caught and imprisoned with Sarah in a storeroom. Escaping in Isabella's old hot air balloon, they arrive at jones's New years festival party and his birthday as he is lighting the candle.
After a struggle, the cake falls to the floor and a bomb inside is revealed. While attempting to dispose of the bomb, Jones and darlyn are attacked by Isabella, who reveals she is the "serial killer" and detests victims and their creations for ruining her figure and her career as the Grimsborough girl after her obesity from consuming too many pastries meant she could not ride her balloon anymore. While attempting to finish off Jones, a battle ensues between Isabella and Sarah in a yellow forklift truck covered by giant gloves.
In the chaos, the bomb ends up in the back of Jones's trunk pant. Darlyn and Sarah neutralize the explosion using a large amount of color paint while Isabella uses the distraction to leap onto her balloon and escape. However, owing to her weight due to eat a cakes, the balloon crashes into the crocodile pit at the zoo where she is eaten alive (off-screen). The balloon floats away with Isabella's ghost (her former teen self) waving goodbye to The teammates crew. Distraught by the death of her mentor, Sarah leaves, with both Darlyn and jones depressed over their losses (though Kai cheers up for them after a good party while Jones is still upset due to naomy is jealous of Isabella). Deciding to take their minds off things, they head out to track a killer down and find Sarah (who was saved by naomy as jones was kissed by naomy.) standing in the driveway, uncertain as to what to do or where to go. She joins them in the van and the teammates crew drive off into the sunset.