- Unknown:
- Michael Kelly
- Production By:
- E. J. King Bull
- Caccini:
- Tom Clarkson
- Jesuit Father:
- Anthony Jacobs
- Vincenzio Fiorenzuola:
- Leon Quarterniaine
- Cardinal:
- John Turnbull
- Galileo Galilei:
- Andre Morell
- First boy:
- Marjorie Westbury
- Second boy:
- David Spenser
- Bonciano:
- Peter Bull
- Giovani Magini:
- William Trent
- Christina:
- Lydia Sherwood
- John Wedderburn:
- John Laurie
- Melchior Inchofer:
- Stephen Jack
- Nicolo Riccardi:
- Charles Mortimer
- Niccolini:
- Leslie Perrins
- Carlo Sinceri:
- Esmé Percy
