What has not been forgotten

June 2019: Dawn in London. Screams echo along the Thames as a bag washes ashore. Its contents: human bones. A murdered young woman whose death occurred many years ago. But why do forensic experts also find microscopic traces of a rare tree species? Detective Samuel Owusu is assigned to the case and follows the clues to a property in Chelsea. It was exactly there that the police found a baby and three adult corpses 30 years earlier. The clues also point to a sibling pair in Chicago - both are desperately searching for the only person who holds the key to their mysterious past. Four dead. A secret. And a family that almost took this secret to the grave.