Lasting just over four days, the Great Smog plunged London into a terrifyingly murky gloom - the acrid pollution seeping into homes, leaving Londoners gasping for breath, shutting down transport and emergency services, and overwhelming hospitals and undertakers alike.

Exploring the fear that paralysed London as the disaster entered day three, focusing on the public not knowing or understanding what was happening, the government's lack of action, to the undertakers working 24 hours a day. As the story concludes, Dr Xand Van Tulleken and Raksha Dave reveal why and how the smog lifted, and London metaphorically and physically began to breathe again.