On a cattle drive Hoppy, camp cook Windy, companion Lucky, and young Artie Peters encounter an eccentric professor. The professor professes to be searching for the evolutionary missing link, but in reality he is a cattle rustler who uses his dynamite to scatter the cattle in order capture some of them. Hoppy and Bar 20 guys ultimately capture the professor.
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Cast:
William Boyd - Hopalong Cassidy
George 'Gabby' Hayes - Windy Haliday
Russell Hayden - Lucky Jenkins
Nora Lane - Nora Blake