Every Day, the last novel I read, I could not put down Emma Healey's Elizabeth is Missing. I read it in two nights, getting about a quarter of the way through it the first night and reading straight through to the end (until 4am!) the second night.
One of the most intriguing things about Elizabeth is Missing is the fact that it's narrated by an old woman with Alzheimer's, so you don't know whether what she's telling you is accurate. In fact, there are many times where in the narration Maud forgets something she told you just a page before, or mixes up the details of the story the second time she tells it.
Elizabeth is her friend in present day, another older woman, and Maud doesn't know what happened to her. She starts looking for her, asking questions and trying to file police reports, and you slowly find out that this has been going on for some time. You also get the feeling that everyone knows what happened to Elizabeth, but because it's told from Maud's point of view, and no one is telling her, you only have the suspicions you are able to piece together from what people tell Maud (stuff that she forgets right away, but of course, the reader doesn't share that problem).
At the same time, though, her flashbacks begin to unravel another mystery, the mystery of what happened to her older sister, who disappeared when Maud was a teen. While we still want to know what happened to Elizabeth, it becomes clear that the real mystery is what happened to the sister, and that is the driving force behind why Maud is always looking, always suspicious. Through the flashbacks, which are remarkable clear compared to her present-day recollections (most of the time), you start piecing together a suspicion of what happened to her.
The narration is beautifully written so that you really feel as confused as Maud. There were times when I would stop reading and actually have a hard time shaking that feeling that I was confused and needed help. The revelation at the end, when it comes, is incredibly satisfying, and it's well worth the rush to the finish line in order to find out what happened to Maud's sister, as well as Elizabeth.
I cannot recommend this one enough!