- Marguerite Courtot
- Marguerite
- Richard Purdon
- Peter Enright
- Edward Roseman
- Ferris - a Broker
- Bradley Barker
- Hal Worth [Ch. 5] / Bob Winters [Ch. 6-16]
- Edwin Brandt
- Dangler - an Adventurer [Ch. 7]
- William Sherwood
- Rudolph [Ch. 6]
- Julia Hurley
- Martha [Ch. 6]
- Phil Hardy
- Fenton - Ferris' Partner
- Helen Lindroth
- Frances - Marguerite's Maid
- Frank Holland
- Leo - Frances' Husband
- Robert Vaughn
- Garrett - Leader of the Kidnappers [Ch. 3]
- Harry Edwards
- Max - one of the Kidnappers [Ch. 3] / Jones - a Foreign Agent [Ch. 10] (as J. Harry Edwards)
- F.B. Vernoy
- Hal Worth [Ch. 4]
- Walter McEwen
- Durbar - an Oriental Mystic [Ch. 4]
- Anna Reader
- Martha - one of Durbar's Victims [Ch. 4]
- Otto Niemeyer
- Carlow - a Fortune Hunter [Ch. 5]
- Freeman Barnes
- Morton - Carlow's Accomplice [Ch. 5] / Manforth - Bolton's Accomplice [Ch. 8]
- Henry A. Barrows
- Bolton - Head of a Band of Crooks [Ch. 8]
- Stella Jenno
- Irene - Bolton's Accomplice [Ch. 8]
- A. Lever
- Gungha [Ch. 9]
- Eleanor Lewis
- Alota - Gungha's Accomplice [Ch. 9]
- Lois Howell
- Bertha - Gungha's Accomplice [Ch. 9]
- R.A. Bennett
- Kagler - Bob's Assistant [Ch. 10]
- Joseph Sullivan
- Wharton - a Foreign Agent [Ch. 10]
- Forrest Cummings
- (as Richard Forrest Cummimgs)
