• 
  Lionel Atwill

  Cyrus Maldor
• 
  Tom Chatterton

  J.C. Henley [Chs. 6-8]
• 
  John Davidson

  Gruber
• 
  Robert Frazer

  Clinton Lyman [Chs. 10-12]
• 
  Lorna Gray

  Gail Richards
• 
  John Hamilton

  G.F. Hillman [Chs. 13-14]
• 
  Russell Hicks

  Randolph
• 
  Edward Keane

  Agent 33 [Ch. 15]

• 
  George J. Lewis

  Bart Matson
• 
  Norman Nesbitt

  Newscaster
• 
  Dick Purcell

  Captain America
• 
  Frank Reicher

  Lyman [Ch. 1]
• 
  Hugh Sothern

  Eldon Dodge [Chs. 2-5]
• 
  Charles Trowbridge

  Dryden
• 
  Crane Whitley

  Dirk [Chs. 11-12]