Eventually, the truth comes out: She is a countess hoping to travel unnoticed. This situation becomes the excuse for Chaney's typical vehicle as the doomed misfit who loves a woman far beyond his station.
Countess Tatiana (Barbara Bedford) arrives in Novokursk to stay with the wealthy Gaidaroff family, and finds Sergei a trivial job at the mansion. But he is not satisfied with this, having been grandly promised that he and Tatiana would be friends forever. He falls under the spell of another servant who is caught up in the dogma of the coming revolution (just wait until you see this actor's grotesque mug). Driven into a rebellious frenzy, Sergei becomes more aggressive with Tatiana. And this is where the film squanders its appeal. We're left without a sympathetic hero. The story would have worked better if it had opened with Tatiana as the main character -- a kind noblewoman who meets a troubled brute while trying to complete a difficult journey. But Chaney was the marketable star, not Bedford.
"Mockery" doesn't test Chaney's acting powers as much as his top work, but the film is short and hence not much of a chore to muddle through.