Rosalind Devlin Timeline & Summary

Rosalind is shocked—shocked—when her sister Katy is found murdered.
She wants to know all the details, and she implores Rob Ryan, the detective, to find out who murdered her sister.
Rosalind calls Rob often, giving him a few details here and there—her dad may be abusive, Katy was a liar.
She arranges a meeting between Rob and Jessica, Katy's near-catatonic twin sister, who says that she saw a mysterious man in a tracksuit near the woods. A man whose description matches that given by another witness.
As the case continues, Rosalind grows increasingly erratic. One minute, she thinks Rob is perfect to solve the crime, the next she's jealous that Rob only cares about Katy, not about her. As if.
When Damien confesses to the murder, and mentions his relationship with Rosalind, Cassie shows up at Rosalind's door.
They go for a walk, and like a supervillain, Rosalind reveals her entire plan: She used to poison Katy, but when she stopped drinking that Kool-Aid, she manipulated Damien into killing her.
Cassie tries to arrest Rosalind, and Rosalind attacks her.
Her whole testimony turns out to be inadmissible since this girl has been lying from the beginning: She's seventeen, not eighteen.
She gets off with a slap on the wrist.