The "Mark of Cain" is a small pattern used in tattooing, which is said to correspond with the tribal mark which Jehovah appointed to Cain in the patriarchal story. This mark is seen upon the body of a nobleman's son, who for the sake of inheriting properly has sacrificed the life of his friend, and by its means he is most ingeniously brought to justice. Scene laid in London. The inventor of a flying machine figures prominently.

This book is annotated with a rare extensive biographical sketch of the author, Andrew Lang, written by Sir Edmund Gosse, CB, a contemporary poet and writer.