After preparing part of a southern California granite quarry for dynamiting the following morning, a work crew leaves the area. Eleven-year-old Bobby Ware and his pal, twelve-year-old Mickey Goodwin, then arrive on their bicycles to explore and play on the heavy equipment. Deciding to climb up to the top of a ridge, the boys hide their bicycles in brush to prevent theft and set off. Upon reaching the top, however, Bobby stumbles and when Mickey tries to catch him, both fall into a ravine, landing on a shallow shelf, halfway down the dangerous incline. When Bobby's father George returns home from work to his wife Janet and younger children Sammy and Janey, Janet tells him that Bobby is late in coming home, but George decides that Bobby may simply have been delayed by a flat tire on his bicycle. Meanwhile, Max Goodwin, Mickey's father, learns from his housekeeper, Sophie, that his son is late for dinner.