Diabolical mastermind Harry Crowel, a.k.a. Prisoner 39013, escapes and, with a seemingly endless supply of henchmen, sets out to destroy all holdings of industrialist Horace Granville, who put him in prison. One target is an amusement park, home of the three Daredevils of the Red Circle, who perform death-defying stunts. Aghast at innocent lives lost, our three heroes swear to capture No. 39013. It'll be harder than they suspect; the villain is holding the real Granville captive, and with a near-perfect disguise, has taken his place!