Alison Waines didn't expect her two-year-old psychological thriller to hit it big.
But it suddenly took off this year, selling tens of thousands of copies, climbing to the top of Amazon.com Inc. 's U.K. and Australian charts for e-book downloads, and becoming a topic of discussion in book clubs.
"I'm making more money than I ever have before," said the former psychotherapist.
The plot twist? Many of Ms. Waines's readers bought the book, "Girl on a Train," by mistake. They meant to buy "The Girl on the Train," the best seller by Paula Hawkins that is being made into a movie starring Emily Blunt and Justin Theroux.