3.3 The Creeping Death by Roy Gill
London, 1952, and a deadly smog envelops the capital.
But something even more dangerous - and alien - is hiding within the mists.
When the Doctor and Donna get lost in the fog, they find a motley group of Londoners trying to make their way home.
Very soon, the stakes are raised, as death creeps along fume-choked streets, and not everyone will make it out alive...