The Overnight — R.L. Stine

WELCOME TO FEAR STREET
Don't listen to the stories they tell you about Fear Street. Wouldn't you rather explore it yourself...and see if its dark terrors and unexplained mysteries are true? You're not afraid, are you?

Nightmare Island
"Nothing bad will happen," Della O'Connor assures her friends in the Outdoors Club. So what if their advisor can't go on the overnight to Fear Island -- Won't it be more fun with no adults around?

But it's no fun at all when Della gets lost in the woods, and the dangerous stranger appears, whispering threats, driving her to a violent act.

Suddenly all of her friends are involved, prisoners in a conspiracy of silence, trying to conceal the terrible truth. But someone saw what Della did. And he's threatening them all, forcing them back to Fear Island to find the evidence they forgot to bury...