Amazon U.K.'s first consumer report of the year has revealed that Paula Hawkins' "The Girl on the Train" topped the e-commerce giant's list for biggest selling e-books of 2015, reported the Book Seller. The intense novel, intertwining themes of marriage, murder and alcoholism, seemed to catch the attention of readers due to its dark and engaging plot.

"The Girl on the Train" focuses on Rachel, who takes a train to London every day, described Neal Thompson on Amazon Reviews. She fixates on a couple she can see from the train and names them Jess and Jason. One day, she sees Jess kissing another man, and the book takes a dark twist after that.

Hawkins' novel falls under a new genre known as "dark psychological thriller." Gillian Flynn's "Gone Girl," a prominent novel that ultimately became a high-grossing Hollywood blockbuster, also falls into that category, according to the Guardian, and the similarities between the two books doesn't stop there, according to some avid readers on GoodReads. Coincidentally, "Gone Girl" also made it onto Amazon U.K.'s best-selling e-books list, hitting fifth place.

In fact, most of the books on the best-sellers list were written by women, including "Grey" by E.L. James (No. 2), "Silent Scream" by Angela Marsons (No. 3) and "Elizabeth is Missing" by Emma Healey (No. 4), as reported by the Guardian.

There were only two books by male writers that made it on the best-selling e-book list: "Personal" by Lee Child (No. 10) and "Us" by David Nicholls (No. 12).

Amazon has continued to be the undisputed leader in e-book sales, though parts of its massive ecosystem are continually being challenged, as previously reported by HNGN.