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.
as Hopalong Cassidy
as Windy Halliday
as Lucky Jenkins
as Nora Blake
as Horace Hepburn
as Laura Peters
as Artie Peters
as Buck Peters
as Blackie
as Keno
as Pete
as Henchman
as Dirk
as Bar 20 Cowhand
as Henchman
as Slim
