Set in Victorian times, Boris Karloff plays a determined writer who becomes obsessed with a twenty-year-old case surrounding "The Haymarket Strangler" and intends to prove that the young man who was hanged for the murders two decades earlier was, in fact, innocent.  All evidence seems to point to a certain Dr. Tenant who used a surgeon's knife to not only choke the life out of his victims, but to slash their flesh as well.  But the details of Tenant's life and whereabouts since the crimes remains a mystery, one which Karloff comes to learn hits closer to home for him than he suspected.

It's amazing to realize that Boris Karloff was nearly 70 when he appeared in this film as it is impressive to see him perform so vigorously in a very physically demanding role.  He is required to undergo very strenuous activity as he contorts his body and facial features to simulate a Jekyll/Hyde madman on the loose -- upper teeth gnawing spasmodically at his lower lip, one eye half-closed, a twisted arm wielding a scalpel.  At more refined times, Karloff is very dedicated in his role as the well-meaning but disoriented author on a road to madness.

There is no question that there are some powerful moments in this feature, and it is highly required viewing for any fan of Karloff.  Unfortunately, the film bears a weight of becoming tedious on occasion, so first-time viewers would want to make allowances for this in between the thrills.