A graveyard, sinister music, a small child's nightmare...

A children's tune played on a hurdy-gurdy

A small boy's nightmare

The same tune played by an old blind beggar outside a foggy graveyard - and heard again by an old, bed-ridden woman

And heard again, at the dead of night on a London street corner

What is the connection - and why is this disturbing melody the prelude to a brutal crime ...