斯蒂芬妮接到好友艾米丽的电话请她帮忙照看儿子。对斯蒂芬妮而言，这只是举手之劳，可谁知艾米丽就此人间蒸发。在寻找艾米丽的过程中，斯蒂芬妮和艾米丽的丈夫肖恩相互帮助，渐生情愫，但他们无法确定艾米丽的生死，更不知能否跨过那条界限。
直至警方在湖边发现一具女尸，通过DNA检测证实为艾米丽……随着女尸的出现，那些黑暗的秘密、对人心的控制和对彼此的欺瞒逐渐显露。斯蒂芬妮的内心被不堪的过往折磨，肖恩无法相信妻子自杀。
至于艾米丽，究竟遭遇了什么不测，还是另有原因让她放弃了完美家庭与人生？秘密可以让人如此亲密，也可以让人身处险境。举手之劳，如导火索般让事态一发不可收拾，将三人命运紧紧绑在一起，成为一生都无法逃脱的“牢”。"
She’s your best friend.
She knows all your secrets.
That’s why she’s so dangerous.
A single mother's life is turned upside down when her best friend vanishes in this chilling debut thriller in the vein of Gone Girl and The Girl on the Train.
It starts with a simple favor—an ordinary kindness mothers do for one another. When her best friend, Emily, asks Stephanie to pick up her son Nicky after school, she happily says yes. Nicky and her son, Miles, are classmates and best friends, and the five-year-olds love being together—just like she and Emily. A widow and stay-at-home mommy blogger living in woodsy suburban Connecticut, Stephanie was lonely until she met Emily, a sophisticated PR executive whose job in Manhattan demands so much of her time.
But Emily doesn’t come back. She doesn’t answer calls or return texts. Stephanie knows something is terribly wrong—Emily would never leave Nicky, no matter what the police say. Terrified, she reaches out to her blog readers for help. She also reaches out to Emily’s husband, the handsome, reticent Sean, offering emotional support. It’s the least she can do for her best friend. Then, she and Sean receive shocking news. Emily is dead. The nightmare of her disappearance is over.
