The girl... Libby's life is going according to plan. She has one free summer before she starts her new job, which means she has time to do a favor for her best friend, Evan. The favor... Libby agrees to keep an eye on Evan's grandma until he can find a permanent companion for her. How hard could it be? But this particular grandma is determined to commit the perfect murder. The match... While Evan and Libby spend the summer protecting the world from Grandma Marcie's murderous plans, they find themselves blurring the fine line of friendship—and there's no going back.