All it takes is one second. One stupid move. One click of a cell phone. When Callie discovers Katherine sprawled on the ground, she bends down to help her. It's only natural—the party's been a bit wild. And it's only natural for her to pull out the fake knife, irritated at one more example of Katherine's callous disregard of other people's feelings. But the knife is real . . . and bloody. And then Callie hears the click of one cell phone, followed...