The Coworker Book by Freida McFadden

"Dawn Schiff is strange. At least, everyone at work thinks so. 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