An Unseen Enemy is probably most notable for being the first film of the Gish sisters, Lillian and Dorothy. It's also a rather good short in its own right, being the latest in a series of increasingly adept reworkings of Griffith's trapped heroine/ride-to-the-rescue drama.
When Griffith first met the sisters, he seems to have been attracted to the idea of casting them as endearing twins, here dressing them identically. It is actually younger sister Dorothy who is foregrounded often literally but Lillian's is the standout performance. She reacts convincingly and lends an air of credibility to an otherwise very hammy melodrama. The worst offender in the hammy stakes by the way is Elmer Booth, who would later give a great turn in The Musketeers of Pig Alley, but here just does the old wide-eyed-panic-in-close-up routine that is the staple of so many silent melodramas.
In spite of the illustrious acting debut, this is still very much Griffith's show, the director having by now honed a precise formula for this type of film. The set-up is rather concise, and the action finale actually takes up around half the picture. Griffith weaves together various different strands to make a four-way crosscut, perhaps his most complex ride-to-the-rescue thus far. He also throws in various little twists to ratchet up the tension the car being delayed by the swing bridge, the phone line going dead and, of course, that menacing gun. It may look rather corny, almost surreal in fact, but there is something very creepy about the close-up in which the gun slowly emerges through the hole in the wall.
An Unseen Enemy is a decent Biograph short, very typical of Griffith's output around this time. Lillian Gish was clearly already one to watch, although it's worth remembering that she only had a handful of big roles in the Biograph shorts, and it was only once Griffith began making features that she emerged as his main leading lady.
