The Couple Next Door by Shari Lapena

PEOPLE ARE CAPABLE OF ALMOST ANYTHING.
'2016's most talked-about new thriller' Stylist
'A twisty, utterly riveting tale that will send readers on a wild rollercoaster ride of emotions. Shocking revelations kept me turning the pages like a madwoman' TESS GERRITSEN
Fast-paced and addictive, THE COUPLE NEXT DOOR announces a major new talent in thriller writing.
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You never know what's happening on the other side of the wall.
Your neighbour told you that she didn't want your six-month-old daughter at the dinner party. Nothing personal, she just couldn't stand her crying.
Your husband said it would be fine. After all, you only live next door. You'll have the baby monitor and you'll take it in turns to go back every half hour.
Your daughter was sleeping when you checked on her last. But now, as you race up the stairs in your deathly quiet house, your worst fears are realized. She's...