It starts with a simple favour – an ordinary kindness mothers do for one another.

When her best friend, Emily, asks Stephanie to pick up her son from school she happily says yes.

Their children are classmates and best friends. And five-year-olds love being together – just like she and Emily. As a widow and stay-at-home blogger mum living in suburban Connecticut, Stephanie was lonely until she met Emily, a glamorous and successful PR executive.

The trouble is that Emily doesn't come back. No matter what the police say, Stephanie knows that she would never leave her son. Terrified, she reaches out to her fellow mummy bloggers.

And she also reaches out to Emily's husband – just to offer her support.

What Stephanie hasn't shared are the secrets buried in a murky past.