The Coworker Book by Freida McFadden

Dawn Schiff is strange. At least, everyone thinks so at Vixed, the nutritional supplement company where Dawn works as an accountant. She never says the right thing. She has no friends. And she is always at her desk at precisely 8:45 a.m.

So when Dawn doesn't show up to the office one morning, her coworker Natalie Farrell—beautiful, popular, top sales rep five years running—is surprised. Then she receives an unsettling, anonymous phone call that changes everything…

It turns out Dawn wasn't just an awkward outsider—she was being targeted by someone close. And now Natalie is irrevocably tied to Dawn as she finds herself caught in a twisted game of cat and mouse that leaves her wondering: who's the real victim?