Hopalong Cassidy and Johnny Nelson ride to the mountains to help a man and his daughter save their logging business from someone who is sabotaging their efforts.

Hoppy, Johnny and California go to Arabia to buy some horses. There they get involved with a sheik and a harem and a kidnapping plot.

Hoppy, California and Johnny come to the ranch of a friend and his daughter, disguised as dude detectives from the east, to investigate the disappearances, without a trace, of several herds of cattle.

Hoppy is leading a scientific expedition and the Chinese who have a hidden settlement nearby are trying to stop them. Saulters and his outlaw gang are also in the area looking for a gold mine. When Saulters men attack, the gold mine is found. Hoppy agrees to file for the Chinese and heads after Saulters in the chase to the land office.

Buck Peters arranges for Hoppy, California, Johnny and other cowboys to go to the aid of friends whose cattle are being rustled. Hoppy and California locate the rustlers' hideout and join the gang by posing as outlaws themselves, but must find a way to let the rest of the posse know where they are.

Jimmy's father, a rancher, died in suspicious circumstances. To make things worse, Jimmy's disreputable uncle has a plot to take over the ranch. Jimmy turns to his friend Brad, the Marshal, for help.

Harry and his pal protect a pretty saloonkeeper from a gang of thugs.