S01E09: 'The Empty Child'
As the Timelord trudges around the streets, Rose becomes distracted by the distant sight of a young boy in a gasmask atop a building crying out for his mummy. She climbs up a rope to reach him, only to discover it's attached to a barrage balloon which quickly starts floating away to fend off an imminent German warplane attack.
The Doctor makes some enquiries at a cabaret club, asking if the residents have seen anything fall out of the sky recently. Much to his embarrassment, he realises that a world war is taking place. Returning to the Tardis, he receives a mysterious phone call from the boy Rose pursued, again asking for his mother.
As he looks for Rose, the air raid sirens begin and The Doctor observes a young woman called Nancy entering a family's house to steal their food whilst the inhabitants unknowingly hide in their shelter. A procession of orphaned children - and a curious Timelord - join Nancy for their stolen feast. However, their meal is soon disrupted as the voice of the child looking for his mother can be heard nearby.
Meanwhile, Rose is floating high above London and struggling to hold onto the rope. Her perilous position - along with her derriere - is being observed by Captain Jack Harkness, an American member of the Royal Air Force. Harkness makes a hasty exit, but as Rose's grip finally breaks, a tractor beam comes out of the sky to halt her fall. The beam comes from Jack's invisible ship and he reels her in to become acquainted. Rose is impressed by the dashing hero and shares a quick dance with him on top of the ship in front of Big Ben.
The Doctor learns from Nancy that a man named Dr Constantine may have a few answers for him at the local hospital - the scene of a mysterious object partially buried in the ground that is sealed off. But the cylindrical craft is not the only thing in confinement, as The Doctor uncovers the effects of a mysterious plague that afflicts the victims with a gasmask face, a scratch on the back of a hand and no signs of life... except they're not dead.
Rose and Jack arrive at the hospital, with the latter being uncovered as a 51st century con artist by The Doctor. But around them, the plague victims spring to life and look to pass on their affliction... and find their mummy.