Inventor Peter Marchmont has discovered a purple light that renders the user invisible. On his release from prison, Marchmont, disguised as Victor Cromport, uses the light to revenge himself against his former wife, Jewel, and her partner, James Dawson, who framed him for theft.
Orphan Enid White becomes the ward of a cruel man. She gets close to her guardian's wife and also to his son, who secretly comes to visit when his father is not around.
Jane Maynard opens a mission in memory of philanthropist Bland Hendricks. John Anstell, son of a powerful and selfish millionaire, Michael Anstell, falls in love with Jane, to the old man's disapproval.
The title is also the moniker of a renowned safe-cracker, Slippy McGee, who has always managed to evade capture until his latest job, when he is wounded.