This one’s creepier and darker than Girl on the Train, though. Under the Harrow by Flynn Berry is the intricate and atmospheric story of Nora and Rachel, two sisters with a close but fraught relationship. One night, on a visit to Rachel’s house in the countryside, Nora finds that her sister has been brutally murdered. Nora is determined to uncover her sister’s killer, and this determination quickly turns to obsession. By the time Nora’s behavior leads to suspicion falling on her, you’re not sure at all whether you can believe what she’s been telling you this whole time.
Nora, our narrator, is extremely unreliable, and you don’t know whether to root for her, dislike her, pity her, or a combination of the three by about two-thirds into the book. By that point you’re not so sure about her sister, Rachel, either.
Berry doesn’t skimp on the descriptions of gore. She evokes an atmosphere of constant cold and rain and unease. It’s a wonderfully tense mystery, with a huge psychological element. The narration, as I said, is skillfully done, and Nora pulls you in even as you’re not sure if you’re getting wrong-footed with her or by her.
Rosamund Lupton’s haunting thriller Sister would be the perfect readalike for Under the Harrow. In that one, Beatrice attempts to solve her younger sister’s mysterious disappearance, and ends up uncovering more than she bargained for. The classic Rebecca by Daphne du Maurier might also be a good choice, if you like uncertain narrators and heavy atmosphere.