Miss Mabel Renshaw is leaving for a visit to her aunt. We are also shown her fiancé, and discover that he is deeply in love with her sister Alice. This does not seem to disturb Miss Renshaw and she proceeds on her visit. This is the last we see of this heiress into whose possession will fall a considerable amount of wealth. Announcement is made that Miss Renshaw has suddenly disappeared and no trace can be found of her. The family go to the famous detective, Griffith Grafton. Before calling upon him they receive a letter from the missing girl, mourning paper being used on account of her father's death. The mother and Mabel's sister, Alice, lay the case before Grafton, showing him the letter, saying she has found the man she loves and is happy and that they should not search for her. Grafton detects a peculiar odor about the paper, he discovers inside the letter invisible writing brought to view by the fire. This discloses that Miss Renshaw, is in trouble, even in fear of death; and pleads for help. The detective keeps this to himself. He soon discovers the secret marriage of Miss Alice Renshaw to Mr. Scott, her fiancé and forces her to confess to it. From all appearances it looks as though Mr. Scott had deliberately taken means to do away with his wife's sister. Mr. Grafton discovers another motive. We are next shown Griffith Grafton, making application at a sanitarium with the assistance of a medical friend. It is also a private insane asylum in which people are confined by force. He soon finds the missing heiress there, held against her will. Her escape is thrillingly shown, and we see a family conference in which the mystery is cleared up and the exposure of the guilty party. Mr. Clark, the respected trustee of the estate, who to cover up his defalcation of the fund had caused Miss Renshaw to be placed under restraint in his private sanitarium.