Arrowsmith by Sinclair Lewis

In the evening, while they returned by Twyford's rattling little motor to Frangipani Court, Mrs. Lanyon talked to Martin as one who had shared his work, but when she had bathed and powdered and dressed, he talked to her as one who was afraid of her. Their bond was their resemblance as brother and sister. They decided, almost irritably, that they looked utterly alike, except that her hair was more patent leather than his and she lacked his impertinent, cocking eyebrow.

Often Martin returned to his patients at night, but once or twice Mrs. Lanyon and he fled, as much from the family stolidity of the Twyfords as from the thought of fever-scorched patients, to the shore of a rocky lagoon which cut far in from the sea.