Kim, Sarah and Melanie are the main antagonists from the children's novel Bad Girls by Jacqueline Wilson.
Kim is a very confident and beautiful leader of this trio and Sarah with Melanie look up to her. The two always try to impress her by taunting Mandy, and they battle each other to please Kim.
The three girls constantly bullied their smart classmate Mandy White whose elderly mother was very overprotective of her and treated her as if she were much younger. Taunting was much worse for Mandy thanks to Melanie who used to be her best and only friend. After Melanie had befriended Sarah and Kim, she revealed them all details about Mandy's life and secret games, giving them perfect chances to make fun of their victim.
Once the bullies circled Mandy at the street and defamed her mother, leading Mandy to claim she is actually adopted and her real parents are very famous. When the girls revealed her lies and started to taunt her even more, it gave Mandy enough bravery to slap Kim's face. She then turned to run, only to be hit by an arriving bus.
After this incident, Mandy's mother found out everything about bullying and informed the school. The headmistress started investigation, but Mandy refused to speak and the bullies only blamed her from lying and slapping Kim. Although there are no other proofs about taunting Mandy, the girls had to promise they wouldn't tell Mandy anything bad anymore. The bullies took it literally and stopped talking to Mandy.
Since then, they were making faces behind her or gossiping her, but never said Mandy's name or anything else to her, so she couldn't prove they were actually talking about her. Instead, they waited for summer to get back at Mandy, as Melanie's and her mothers decided Mandy would visit Melanie every day her mother is at work. Luckily for Mandy, this actually never happened.
Next school year, Mandy's class got a new teacher, Miss Moseley. As soon as she saw Kim, Sarah and Melanie all sitting at the same desk, she told Kim to sit elsewhere, splitting her up with her two minions. After a class discussion about bullying lead by Miss Moseley, Sarah ad Melanie regretted what they had done, and broke up with Kim definitely, leaving her alone and unable to revenge anyone.