Cornell Woolrich 
I Married a Dead Man 

Pregnant, abandoned by her lover, and desperate, Helen boards a train heading west. She meets Patrice, a happy young expectant mother who’s traveling with her husband, Hugh, to meet his family for the first time. Patrice lets Helen try on her wedding-band—just before the train crashes, killing Patrice and Hugh. Thinking Helen is their widowed daughter-in-law, Hugh’s family welcomes her into their rich and loving home. For the first time, Helen’s life is good—until her ex-lover comes to town with blackmail on his mind.

The films J’ai épousé une ombre (1983) and No Man of Her Own (1950) starring Barbara Stanwyck are based on the book.