more from Nancy, but the boy in the gas mask knocks at the door. Nancy orders the children to leave by the back entrance, and warns the Doctor not to touch the boy. The Doctor opens the door anyway, but the child is gone. The Doctor catches up to Nancy and convinces her to give him more information. Nancy reveals that she knew the cylinder fell near a nearby hospital, and its appearance is tied to the boy. The Doctor arrives at the hospital and discovers several patients wearing gas masks fused to their bodies. Dr Constantine explains that Jamie, Nancy's brother, was the first patient with this symptom. Suddenly, Constantine changes into another gas mask-wearing person, and the other patients all rise to start chasing the Doctor. Rose and Jack arrive and quickly escape with the Doctor. The Doctor forces Jack to admit that the crashed cylinder is just a worthless Chula medical transport. The three are trapped in a room as the converted patients converge on them, all asking "Are you my mummy?" Nancy, who had returned to the home to get more food, is also cornered by Jamie, the boy, as he reaches out to her. Production This episode had the working title "World War II". Early versions of this script quoted this episode's title as being "An Empty Child". This is a reference to "An Unearthly Child", the very first episode of Doctor Who. The episode's television listings information and the DVD cover also mention that "London is being terrorised by an unearthly child". In Davies's initial pitch, Captain Jack was originally called 'Captain Jax', an interstellar alien soldier. The name Jax was eventually dropped, as was Jack's original characterisation, instead being a human conman from the 51st century. The filming took place during the fourth production block. Special effects shots were completed at Unit Q2 in Newport on 17 and 18 December 2004. From 4 to 8 January and from 11 to 14 January scenes at Cardiff Royal Infirmary were filmed. On 9 and 10 January scenes shot in alleyways were filmed in Womanby Street, Cardiff. The bar scenes were also shot on 10 January at Headlands School in Penarth. The scene in which Rose hangs from the barrage balloon was filmed in a hangar at RAF St Athan and then in the Vale of Glamorgan, on 17 January. From 18 to 20 January filming