The story starts with an everyday event - a WhatsApp message to a group set up by mums at the school gates to discuss missing jumpers and school trips.
But this message contains a video of a little boy being sexually abused. And one of the group members happens to be a BBC radio producer.
So begins an investigation into the dark world of child sexual exploitation as she tries to find out what happened to the boy. Has he been rescued? Is his abuser in jail?
Along the way she meets the police trying to combat the online proliferation of images and videos of children being abused - millions are in circulation, shared on social media platforms as if they are funny cat memes. She asks what we should do about the 450 men arrested every month for viewing and sharing this material. At the moment, end-to-end encryption means WhatsApp is a safe haven for offenders - are the tech firms doing enough?
Producer/presenter: Lucy Proctor
When a BBC journalist is sent a child sex abuse video, it sparks an investigation.