Frankie Stein and the New Ghoul at School is the second book in the Monster High Diaries book series.
Frankie joins Draculaura and Clawdeen for a sleepover to pick out new outfits for the Fall Scaremester. They discuss that Headmistress Bloodgood is looking for students to guide some new Monster Exchange students that are joining after the break, and Frankie decides she wants to help out. She then remembers that they were given a project to complete over the break, to create a presentation which shows what their lives are like outside of school.. and Frankie had been unable to come up with an idea for her presentation. With only four days left to complete it, the ghouls suggest that Frankie ask her parents for ideas. Frankie hits on the idea of creating something with her father in his laboratory, which she can present to the class.
Frankie asks her parents about her plan, and her father is delighted to work with her. After showing her his lab and explaining safety rules, Frankie suggests that they create a new pet like Watzit, to be his friend. (after suggesting they create a little sibling for her.) Over the next few days and with some spare parts laying around the lab, the two create a creature which Frankie names Zappit. Frankie is delighted with her success, and is even more excited when she learns she will be guiding a new Exchange student, Isi Dawndancer.
The next day, Frankie wakes to discover Zappit is missing. She calls her friends and parents to help her look for her, but they are unable to find her. Worried about her safety and about not being able to bring her to her presentation, Frankie tries to keep positive by looking forward to meeting a new friend. She meets Batsy Claro and Kjersti Trollson, who are already paired with Venus and Ghoulia, and Isi herself. The two get along quite well, as Isi reveals that she came to Monster High thanks to a meeting with Twyla, and that she is already missing her large family at home. Frankie remarks that she'd love to have a large family like Clawdeen has.
The time for the presentation arrives, and despite not having Zappit to show to everyone, Frankie's presentation is well received. After the class, Isi tells Frankie that she saw Zappit last night when she was dancing in the forest, and offers to help Frankie find her. Frankie is delighted, and invites Isi to join her and her friends for lunch. She's surprised, and a little hurt, when Isi declines because she wants to meet Twyla.
The ghouls, along with the Exchange students, meet after school to look for Zappit in the forest, but are unable to find anything except some tracks and a den. After helping her father make a tracking device to look for her, Frankie returns to school, where Isi confesses that she actually saw Zappit last night, when she returned to the forest to do some dancing. Zappit danced with her, and being with her helped Isi feel a little less homesick. Sensing that she might be shy, Isi made her a little den in the forest to sleep in, and offers to take Frankie to her. Frankie is excited about finding her and taking her home to meet Watzit, but Isi suggests that Zappit may actually prefer to be alone than be with others, which Frankie hadn't considered. When Isi bring Zappit to Frankie's home that night, Frankie does note that Zappit is reluctant to play with Watzit.
After Isi goes home, Frankie suggests to her parents that they could create another pet to keep Isi company. As her mother comments on how well she and Isi are getting along, Frankie admits that she feels jealous since Isi seems to spend more time with Twyla. She had hoped she and Isi would become really close friends. Her mother reminds her that she can't be friends with everyone, and should be happy that Isi has made a close friend.
The next morning, Frankie awakes to discover Zappit has disappeared again, and realizes that maybe she really does prefer to be outside, and that she shouldn't force her to get along with Watzit. She meets Isi, who tells her that Zappit has returned to her den in the woods. Now realizing that Zappit and Isi have a close bond, she asks if Isi would like to take care of Zappit. Isi is happy to accept, and invites Frankie to a bonfire party to say thanks.
Frankie joins her friends at the bonfire, where Isi thanks her for being such a good friend, and reminds her that even though she doesn't have a big family, her friends are very much her own pack.