Charles Quigley

Duncan Richards

Linda Stirling

Diana Farnsworth

Clayton Moore

Louis Ashe

I. Stanford Jolley

Dr. Blackton [Ch. 11]

Kenne Duncan

Dr. Chambers [Chs. 1-2, 8]

Forrest Taylor

Prof. Van Wyck

Emmett Vogan

Anderson [Chs. 1-4]

Sam Flint

Maxwell

Joseph Forte

Prof. Parker (as Joe Forte)

Stanley Price

Count Fator [Chs. 11-12]