Haunted . . . or tricked?

The Unicorn Club is throwing the best Halloween party Sweet Valley Middle School has ever seen! Lila Fowler's dad had lent the girls a run-down old shack in the woods - a perfectly spooky place for the party.
But as the Unicorns are fixing the shack, strange and scary things happen: Ellen Riteman discovers a human skull, Jessica Wakefield gets lost in a cave full of bats, and a mysterious girl appears out of no where to relay gohstly warnings.
Rumors are flying that the shack was built over an ancient Native American burial ground. Could the shack really be haunted? Or are the Unicorns the victims of a terrifying Halloween trick?

Stay away . . .

The girls were sitting in a circle around the Ouija board in the Wakefields' dimly lit living room.
Jessica's fingers rested lightly on the marker that was placed in the middle of the board. Letters from the alphabet ran along the perimeter of the board on two sides.
"What are we supposed to do besides sit here?" Lila whispered. "I mean, staring at this marker is getting kind of boring."
"Shhh," Ellen hushed her. "We have to wait for the spirits of Sleepy Hollow Road to send their message."
Suddenly, the marker began to shake and vibrate. Then it shot toward the S.
"It's working," Kala said with a gasp.
"Shhhh," Janet warned.
The marker slid toward the T.
"S T," Mandy whispered. "It's spelling something."
The marker began to dart crazily around the board, furiously spelling out words.
"'Stay'!" Mandy cried. "It spelled 'stay.'"
The marker skidded over to the A. And then in rapid succession it slid to W, back to A, and then to Y.
The girls looked at eachother in silence.
"'Stay away'?" Mary said quietly.

The Secret of the Magic Pen