The Five, a Mary MacIntosh novel

A serial killer, who commenced his murderous rampage before the ripe of age 12, but due to a loophole in the law, is released from juvenile detention. Mac hosts a reunion for her four college roommates at her family cabin in Colorado, and the killer shows up and captures each of the five telling them that one of their husbands hired him to kill her. Each must convince him that she's not it.