Baron Adelbert Gruner is an Austrian nobleman. The Baron is a roguish and sadistic man, a philanderer and a murderer who "collects women" and and chronicles his conquests in a book.

After leaving continental Europe under suspicion of killing his first wife, he moves to England. His courtship of Violet de Merville brings him to the attention of the great Sherlock Holmes, who is hired to cause Violet to end the engagement on behalf of an unknown client. The Baron had previously destroyed the life of Kitty Winter, his last mistress. She wants revenge on him and after helping Holmes in any way she can, she throws vitriol in his face, which leaves him hideously disfigured.