1913. Unmarried sisters Nellie and Vivian Marsh live an impoverished existence in a tiny cottage on the banks of the Little River in Suffolk. Their life is quiet and predictable, until a sudden flood throws up a strange fish on their doorstep and a travelling man who will change them forever.

1939. Eighteen-year-old Birdie Farr is working as a barmaid in the family pub in London. When she realises she is pregnant she turns to her mother Nellie, who asks her sister to arrange an adoption for Birdie's new born daughter. But as the years pass Birdie discovers she cannot escape the Marsh sisters' shadowy past - and her own troubling obsession with finding her lost daughter will have deep consequences for all of them . . .