A young railyard mechanic who completed high school while working wrestles with whether to accept a predictable engine career or pursue wider ambitions; family obligations and loyalty complicate the choice. When trouble on the mountain short line — accidents, dangerous tunnels, a sabotaged timber raft and a runaway special — threatens lives and railroad operation, he faces tests of skill, discipline and courage. Through resourcefulness, teamwork and decisive action he navigates physical hazards and interpersonal challenges, resolves crises that imperil the line, and meets a final contest that determines his standing and future prospects.