The Extra by Annie Neugebauer

Ten people head out on a backpacking trip, but the first night eleven set up camp. Everyone remembers everyone else. Who is the extra?

"The Extra is exceptional in every way: Extra unnerving, extra eerie, extra tense. Annie Neugebauer pedals in the same alpine paranoia as John Carpenter's classic The Thing, manifesting a sense of dissociative anxiety that only mounts with every turn of the page." - Clay McLeod Chapman, author of Wake Up and Open Your Eyes.