The Unknown is an important film for several reasons, which I'll consider in a moment, but its plot, unfortunately, isn't one of them…. [It] is a variant of the beauty and the beast theme, with the beast this time (Chaney) being a bitter and vengeful knife-thrower in a Madrid circus named Alonzo. He is apparently armless and propels his knives at Nanon, his beautiful partner, by means of his toes….

The skill with which [The Unknown] spins a fabric of suspense illustrates the fine technique of director Tod Browning. He never achieved the fame in this field that Alfred Hitchcock has, perhaps because the quality he stresses most in his convoluted plots … is irony, and irony leaves the viewer with an unsatisfied and thwarted feeling. Hitchcock eschews it, and occasionally uses humor. Browning never did. (p. 452)

The Unknown is not a horror film, at least not in the sense that The Hunchback of Notre Dame and Phantom of the Opera are. There's no mutilated or supernatural creature going haywire and wrecking his vengeance on society. The Unknown is a suspense film, with suspense beginning almost in the first few feet, which show the circus tents flapping wildly in the night wind, and resembling shrouds. The lighting is somber throughout, except in the scenes in which [Nanon] appears, which are all illuminated, so that light becomes her leit-motif (her image in Alonzo's eyes).

Many Browning trademarks are in The Unknown: the circus is made to seem the sinister outside world in microcosm; man is made to seem a creature bent on its own undoing; and the heart's impulse toward love is made to lead ironically to tragedy.

Browning's camera was a fluid one, remarkably so for the time. Though there are no tracking shots, he packed so much action in front of his lens the camera seems non-stationary, and becomes successively the eyes of the characters. Of Alonzo, as he spies on the girl he secretly desires, and watches her receive the attentions of others; of Nanon, as she peers down from the wagon window, over the shoulder of her father's assassin, and sees the tell-tale thumb; of the dwarf, as he watches in amusement while Alonzo unconsciously smokes a cigarette he holds with his toes, forgetting his hands have been freed from the straitjacket; of Alonzo again, as he surveys the hospital room where the dreaded operation is to be performed.

The camera reveals some fascinating sights in The Unknown. As the dwarf painstakingly unties Alonzo's straitjacket and we see that the knife-thrower isn't armless at all, we also see how Chaney attained one of his most realistic effects. For the murder scene Browning hemmed the camera in between two towering circus wagons, to add claustrophobia to the victim's fears. The climactic scene in the theatre is brilliantly lit and totally theatrical, with quick cuts from Nanon in a costume made up mostly of white beads, to the increasingly alarmed Malabar, to the galloping horses, to the audience, unaware of what's happening on stage.

Every scene builds upon the preceding one with utmost economy. Nothing is wasted, nothing is superfluous. The pace never falters, and the number of title cards in The Unknown is surprisingly small. (p. 453)