Bar 20 ranch hand Johnny Travers (Jay Kirby) sends for old friends Hopalong Cassidy (William Boyd) and California Carlson (Andy Clyde). Hopalong Cassidy immediately suspects mine company president Dan Slack (Victor Jory) to be behind the rustlings and decides to go undercover, with the assistance of Sharon Longstreet (Shelley Spencer) and her young brother Bobby (Bobby Larson).[4]