Dean R. Koontz - Eyes of Darkness (1996)

A mother sends her son on a camping trip with a leader who has led this trip into the mountains 16 times before without mishap; that is until this time.

Every single camper and leader and driver die with no explanation. As the grieving mother who is the protagonist begins to accept the fact that her son, Danny, is dead she starts getting vicious bully-like attacks from nowhere saying he is not dead, such as writing on chalk boards, words from printers and other various signs.

Along with her new friend, Elliot Stryker, Christina Evans sets out to find out what could have possibly happened on the day that her son apparently died.