“I’m trying to find the name of a young adult horror book in which a group of kids go on a trip (and of course they all start dying one by one). I remember that the girl responsible for the deaths wore horn-rimmed glasses, and first set her plans in action by spiking the hot cocoa of their (bed and breakfast or hostel) hosts with laxative, causing them not to be able to accompany the group that day. She also killed one of the characters with a flare gun. Any ideas? Thanks!”