What a terrific read

I had read so many positive reviews and comments from my friends here that I got really curious and requested this book myself. So, I thank Netgalley and Amazon Publishing UK for this ARC but all opinions expressed in this review are my own. I was certainly not disappointed, the book was even better than I imagined. I think it's the best story that I've read this year.
At the start of the book, we're introduced to Nina and Maggie, who share a house on an estate somewhere in England. Maggie is confined to the attic where she has little else to do than read and look down to the neighbours on the street that can't see her through the shutters. Every other night Nina brings her downstairs to share a home-cooked meal but it's clear that she resents Maggie and cooks things she knows that the other woman dislikes. She can't trust the older woman with sharp instruments and removes a spring, a corkscrew and a loose screw for both their safety. Also, she removed her watch and clock as punishment for a transgression. Apparently, this situation exists for at least two years and however Maggie resisted openly at first by now it looks as if she's adapted (but not accepted) to it. She still tries to escape every time she sees a slight opportunity. Then drops the bombshell, Maggie is Nina's mother and she's a captive, chained to the floor of her bedroom in the attic.
What's going on here? Nina isn't an evil or cruel person, she gives her lunch to a homeless woman that comes to the library for warmth while reading 'Mills & Boon' (I actually knew a woman here in Antwerp who used to do the same, although she had a better taste in books). Why does she treat her mother is this despicable, inhumane way? Nina is convinced that her mother did something horrible and unforgivable to her but we're not told what it is
We dive 25 years into the past to the time when Nina's dad left his wife and kid and just disappeared into thin air. Nina blames her mother for this loss Around that time, she's 14 and starts acting out by getting drunk and staying out half of the night. After she has a (secretly induced by her mother) miscarriage she starts an affair with a much older, popular local rock singer that later will end up in jail for murder.
Little by little, we become aware that there are important events that the daughter has forgotten and the mother keeps silent about. Some of these secrets are hinted at so that you just have an inkling of what may have happened. The tension slowly builds up and you keep wondering if Maggie will eventually escape or even be released (not likely) and also what are these awful unforgivable crimes that Nina accuses her mother of and what happened during the periods that she can't remember? Slowly, one by one those secrets are revealed and some of them are really evil, others merely cruel, I thought repeatedly 'wow, I, didn't see this coming', other things I saw coming or guessed from the hints given. This surely is one messed up, twisted family. And I can understand how Nina feels that some of the things her mother did, no matter how well her intentions were, are completely unforgivable. Nevertheless, her own actions out of resentment aren't defendable neither. It's a twisted page-turner where you're kept in suspense until the very end.