Charles Quigley as Duncan Richards

Linda Stirling as Diana Farnsworth

Clayton Moore as Louis Ashe

I. Stanford Jolley as Dr. Blackton [Ch. 11]

Kenne Duncan as Dr. Chambers [Chs. 1-2, 8]

Forrest Taylor as Prof. Van Wyck

Emmett Vogan as Anderson [Chs. 1-4]

Sam Flint as Maxwell

Joseph Forte as Prof. Parker (as Joe Forte)

Stanley Price as Count Fator [Chs. 11-12]

Wheaton Chambers as Wilson [Ch. 1]

Tom Steele as Henchman Stricker [Chs. 4, 7, 9]

Dale Van Sickel as Henchman Harte [Chs. 6-7]

Rex Lease as Bain

Fred Graham as Snyder [Chs. 1-2] / Zane [Ch. 8]

Bud Wolfe as Cross - Apartment Thug [Chs. 11-12]