The thriller unfolds in a pioneer camp near the Wonderful Lake, shrouded in mysterious legends about a hidden treasure and spirits inhabiting the depths of the forest. From the first days of the third shift, the children develop a strange feeling: deep in the lake they see ghosts, and the forest seems to come alive, not letting them escape. At night, a group of boys from the first squad secretly makes its way to the lake, where one of them brings a bloody vow, seeking to win the friendship of the leader. After that, he changes completely—turning from a modest, timid boy into a confident, audacious one. The next morning, the camp discovers the body of a counselor with no signs of life.