The Way in the Dark — Jean S. MacLeod

You can't go back! You can't go back! The train wheels repeated their message. yet after six years of comfortable living, an undeniable compulsion was drawing Janet back to the bleak, isolated Yorkshire farm. Back to Mark, whose young love she had rejected. Now she realized he was the only man she would ever love. But Mark had changed. Bitter and unforgiving, he was not interested in her own reasons for returning-- only that she was there to work.

Hero: Mark (step-brother)
Heroine: Janet Landon