Becca Bell is the hidden main villainess of the YA mystery novel A Good Girl's Guide To Murder, written by Holly Jackson.
Becca was introduced as the sister of local schoolgirl Andie Bell, who five years prior to the events of the novel, disappeared and was believed to be have been murdered by her boyfriend Salil Singh, who then apparently committed suicide. Main protagonist Pippa 'Pip' Fitz-Amobi, owing to her friendship with Salil decides to look further into the case as part of her senior project, enlisting the help of Salil's younger brother Ravi to do so.
Throughout the novel, Becca appears to still be grappling with the traumatic events of her sister's disappearance, and Pip soon learns of the Bells' father Jason's emotionally abusive behavior towards his daughters, as well as the fact that Andie was secretly a drug-dealing villainess. As Pip continues her investigation, she begins to receive threatening notes, culminating in her dog Barney being abducted and held for ransom in exchange for the laptop containing her notes on the case. Rather than uphold their end of the bargain, the villainous ransomer drowns Barney in a river.
Eventually, it was revealed that history teacher Elliot Ward was responsible for Salil's death, having been having an affair with Andie that ended in her running away from him in the middle of the night and never being seen again. Elliot also abducted a woman who he believed was Andie and kept her imprisoned in an abandoned house for the five years that passed.
Sometime following this revelation, Pip goes to visit Becca following the Bells' mother checking herself into therapy following the discovery of Elliot's actions. While there, Pip realizes that Becca is the one responsible for Andie's disappearance.
As Becca revealed, shortly before Andie vanished, Becca had been drugged and raped by a schoolmate named Max Hastings, who used roofie drugs supplied to him by Andie. When Andie arrived home following her confrontation with Elliot, Becca confronted her sister and pushed her over, resulting in Andie dying from choking on her own vomit. Becca then further turned heel by dumping Andie's body in a septic tank, and leaving her car parked outside the house of her drug dealer in order to frame him, the same number plate written on Sal's notes app. She says that she let Barney go, but he drowned himself, at least that's what she thought. In reality, Jason Bell had killed the dog, thinking it was Becca's. When he discovered that it wasn't her dog, and it was Pip's, he became even more happier.
At that moment, Pip began to feel the effects of a drug that Becca had placed in her food. Becca began to make her move to kill Pip in order to silence her. However, Ravi and Pip's parents follow them into the woods, and were able to subdue the evil Becca, saving Pip's life.
In the epilogue, it was revealed that Becca was sent to prison for her crimes. However, Pippa and Becca become friends and call each other weekly. Becca also helps Pippa by giving her the name of Andrea/Andie Bell's first hamster to answer the security question needed to unlock Andie's secret email account, which helped Pip in uncovering the secret about "a man who eats dinner with them" and is "toxic", and is moreover the DT Killer. The email shows Andie's love for Becca and her attempts to save her and take her away from "him". Becca and Andie did have a strained relationship, and this reason in the email played a crucial role in Andie's death, as she couldn't let anything else come in the way and didn't want her