Gripping stories from the shadows - BBC investigations from across the UKThe inside story of how ancient treasures disappeared from one of the world's most famous museums. And how one man believes he uncovered a thief.BBC Culture Editor Katie Razzall reveals how a Danish gem dealer almost single-handedly identified a man he believes had been stealing precious artefacts from the British Museum. She looks at why thefts went unnoticed for so long.What begins as a whodunnit turns into a global treasure hunt as Katie tries to track down the missing gems.