The Dark Other by Stanley G. Weinbaum

Pat turned the envelope dubiously in her hands, while a maze of chaotic thoughts assailed her. She felt almost a sensation of guilt as if she were in some manner violating the promise given to Dr. Horker; she felt a tinge of indignation that Nicholas Devine should dare communicate with her at all, and she felt too that queer exultation, an inexplicable pleasure, a feeling of secret triumph. She slipped the letter in the pocket of her robe and padded quietly up the stairs to her own room.

Strangely, her loneliness had vanished. The great house, empty now save for herself and Magda in the distant kitchen, was no longer a place of solitude; the discovery of the letter, whatever its contents, had changed the deserted rooms into chambers teeming with her own excitements, trepidations, doubts, and hopes. Even hopes, she admitted to herself, though hopes of what nature she was quite unable to say. What could Nick write that had the power to change things? Apologies? Pleas? Promises? None of these could alter the naked, horrible facts of the predicament.