Big Little Lies by Liane Moriarty

Jane hasn't lived anywhere for longer than six months since her son was born five years ago. She keeps moving in an attempt to escape her past. Now the idyllic coastal town of Pirriwee has pulled her to its shores and Jane feels as if she finally belongs. She finds friends in the feisty Madeline and the incredibly beautiful Celeste, two women with seemingly perfect lives - and their own secrets.

But at the start of a new term, an incident involving the children of all three women occurs in the playground, causing a rift between them and other parents. Minor at first but escalating fast, until the whispers and rumours become vicious and spiteful, and the truths blur into lies.

It was always going to end in tears, but no one thought it would end in murder...