None of This is True by Lisa Jewell

Celebrating her 45th birthday at her local pub, podcaster Alix Summer crosses paths with an unassuming woman called Josie Fair. Josie is also celebrating her 45th.

A few days later, they bump into each other again, this time outside Alix’s children’s school. Josie says she thinks she would be an interesting subject for Alix’s podcast. She is, she tells Alix, on the cusp of great changes in her life.
Alix agrees to a trial interview and indeed, Josie’s life appears to be strange and complicated. Aix finds her unsettling but can’t quite resist the temptation to keep digging.
Slowly Alix starts to realise that Josie has been hiding some very dark secrets, and before she knows it Josie has cajoled her way into Alix’s life – and into her home.

Soon Alix begins to wonder who is Josie Fair really? And what has she done?