Acting on a dare, the friends decide to find out the basis for a story that has circulated throughout the town for generations: that there is a monster living at the top of McMurphy's Mountain. Though the boys are not sure they believe in the legend, they are still a bit scared.
Soon, the boys come upon an old shack, so they make camp for the night, taking shifts sleeping just in case the monster is lurking about. What they find in the shack is very unexpected and changes a camping trip into a strange adventure.
Now, the boys wonder whether they should have ventured up the mountain. But they press forward with their journey, finding more secrets and the truth about the mountain they feared.