A young civil engineer working on mountain railroad construction contends with hazardous trails, sudden storms, and a confrontation with a former enemy. When word arrives that his close friend Jessie Wadsworth and his sister Laura have vanished, he launches a determined search that threads mountain camps, mining towns, and broken trails. Clues accumulate—letters, local informants, and a fragment of horsehair—leading to perilous rescues, tense captures, escape attempts, and a final roundup that resolves the disappearances and reunites those involved.