His countenance instantly assumed an aspect of the deepest gloom, and he replied, "To seek one who fled from me."
Letters, Letter 4 · Victor Frankenstein
Context
When Walton's lieutenant asks why Victor traveled so far onto the ice, Victor's face darkens and he explains he is pursuing someone who ran from him.
Analysis
The shift from "countenance" to "deepest gloom" works as instant emotional weather—Victor's face becomes a landscape that darkness moves across. Shelley uses this image of encroaching shadow to make Victor's inner state visible and uncontrollable, as if grief and rage are external forces that possess him rather than emotions he chooses to express.
Essay Tip
Use this to argue that Shelley depicts destructive emotion as something that colonizes a person from within—the gloom "assumes" control of Victor's face, grammatically making him the object rather than the agent, which captures how revenge has taken over his will.