When Edyth Vail trails her loving but distracted fiancé Allen Morris and stumbles upon the murdered body of David Hume, she suspects that Allen has committed the crime and immediately contacts Ashton-Kirk, a noted sleuth. After some careful investigation, Kirk uncovers the fact that Hume was killed while protecting a safe hidden behind a picture, and that Allen's father, an inventor, had recently drawn plans for a new submarine. Allen finally admits that he had gone to Hume's room in hopes of retrieving the papers Hume had stolen from his father, but upon discovering the man dead, had panicked and left. With the help of a train conducter's ticket punch, Kirk tracks down the identity of the murderers and sets a trap for them at the safe. As predicted by Kirk, the killers, one of whom is a mute, show up to break open the safe and are apprehended by the police.

Director:
Ashley Miller	Director
Arnold Daly	Director
Cast:
Arnold Daly	as Ashton-Kirk
Sheldon Lewis	as David Hume
Louise Rutter	as Edyth Vail
William Hartigan	as Allen Morris
Charles Laite	as Pendleton
Producer:
Arnold Daly	Producer

This film was the second production in a series called "Ashton-Kirk, Investigator," the first being An Affair of Three Nations. William Hartigan was also listed as William Harrigan in one source.

Based on the short story "The Menace of the Mute" in Ashton-Kirk: Investigator by John Thomas McIntyre (Philadelphia, 1910).