Enroute to Borderville, looking for his father's killer, Bob (Bob Steele) stops a runaway horse carrying Mary (Claire Rochelle.) His pal Dan (Kit Guard), who has followed Bob against his orders not to, has a fight with one of Lambert's henchmen, Frank (Bob Walker) which Bob stops. In a Borderville tavern owned by Buck Lambert (Ted Adams),who is engaged in smuggling contraband across the border, Bob is taken prisoner by Lambert's men. Notified by Mart, Herbert Crenshaw (Carleton Young) and his men arrive and claim that Bob is a cattle rustler known as "El Diablo" and take him to the Crenshaw ranch. He is released as this was a ruse to save him from Lambert. Mary, working as a cashier at the tavern, informs Crenshaw that Lambert is preparing to run contraband across the border. Bob, seeing Crenshaw embrace Mary, believes they are sweethearts but they are brother and sister working as federal agents. Lambert discovers Mary writing a note to Crenshaw and Bob arrives just as she is making a break. Bob, having discovered that Lambert was his father's killer, captures him and leaves him guarded by Dan while he and Crenshaw ride to intercept Lambert's men henchmen in the pass. But Lambert escapes and takes Mary as a prisoner.