The Grimmer family moved from the UK to Australia in 1969. They were "ten pound poms" - part of a huge wave of migration down under. Months later, Three-year-old Cheryl Grimmer disappeared from Fairy Meadow beach in New South Wales. She was never seen again. In the moments before she vanished, she was being looked after by her oldest brother, Ricki. He was just seven. This is the story of that day, and of its impact in the months, years and decades that followed. It's Ricki's story - his desperate search for answers, and his battle with guilt. And it's the story of an extraordinary police enquiry that was dramatically re-started almost 50 years after Cheryl was taken.
BBC News Correspondent Jon Kay has been investigating the case in Australia and in the UK since 2016. With exclusive access to the family and the investigating officers, he begins an eight-part exploration of this moving, gripping tale.
Produced for BBC Audio in Bristol by Chris Ledgard Music: Elizabeth Purnell Studio engineer: Jacques Sweeney Editor: James Cook