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. CAST: David Tennant (The Doctor), Catherine Tate (Donna Noble), Lauren Cornelius (Ivy Clark), Theo Stevenson (Terry Hopkins), Kieran Bew (Richard Cooper), Stephen Critchlow (Malcolm Wishart), Helen Goldwyn (Alice Aiken / Fumifugium). Other parts played by members of the cast.