Samuel Keifer
Dr. Keith Simms
Dr. Bennett
Professor Sorvad
Lionel Huxley (1 episode)
Dr. Philip Grigg (1 episode)
Gervaise de Lutrelle (26 episodes)
Solicitor (1 episode)
Julian Roberts
Mr. Scanlon (1 episode)
The Hon. W. H. Lyttelton (4 episodes)
Leutnant Hicks (4 episodes)
Richard Barwell (8 episodes)
Hugo Brayford (4 episodes)
Dr. Greg Miller (165 episodes)
Engineer
Ed Jarvis (1 episode)
Francis Considine