Poisonous

Poisonous is another winning novel in the electrifying Max Revere series from New York Times bestselling author Allison Brennan.
Teen-aged Internet bully Ivy Lake fell off a cliff and few people cared ... except her mentally-challenged eighteen-year-old step-brother, Tommy. He loved her in spite of her cruelty. He's distraught and doesn't understand why his blended family is falling apart. After a year, the police still have no answers: Ivy could have jumped, could have been pushed, or it could have been an accident. With too many suspects and not enough evidence, the investigation has grown cold.
Tommy thinks that if someone can figure out what happened to his step-sister, everything will go back to normal, so he writes to investigative reporter Maxine Revere. This isn't the type of case Max normally takes on, but the heartbreak and simple honesty in Tommy's letter pulls her in. She travels to Corte Madera, California, with her assistant David Kane and is at first pleased that the police are cooperative. But the more Max learns about Tommy and his dysfunctional family, the more she thinks she's taken on an impossible task: this may be the one case she can't solve.
If Ivy was murdered, it was exceptionally well-planned and that kind of killer could be hiding in plain sight ... planning the next act of violence. Max believes the truth is always better than lies, that the truth is the only thing that matters to gain justice for victims and their families. But for the first time, she wonders if this time, the truth will kill.