S02E12: 'Army of Ghosts'

The Doctor takes Rose back to London to pay her mother Jackie a visit, only to discover that the planet is in the grip of 'ghost' fever. At certain times of the day, shadowy figures appear on the earth and it's widely believed that these are ghosts, with Jackie under the impression that the shady, faceless figure in the kitchen to be her grandfather. The Doctor believes that the supposed ghosts are some unknown form who are tapping into the desires of those humans nearby to make them see, hear and smell what they want to.

In a towering building a large lever is pulled that coincides with the end of the ghosts' brief daily spell on the planet. It's later revealed that the location is Torchwood HQ, an institute set up by Queen Victoria to capture alien technology, and now run by Yvonne Hartman. Within the building is a large black sphere that contains apparently no mass, yet is floating in the air. Scientists, including Dr Rajesh Singh, are baffled by its existence and purpose.

Meanwhile, two Torchwood employees - Adeola and Gareth - decide to take their flirtation to a discrete, cordoned-off area of the building for some privacy. Gareth slips back to the office leaving Adeola unaware of his whereabouts, so she looks for him in the out of bounds area. Suddenly, from behind the plastic sheets a figure lunges at her and Adeola screams out in agony. The metallic face briefly glimpsed reveals the presence of cybermen within the building.

The Doctor locates the source of the energy controlling the ghosts' presence and decides to investigate. Following the signal's location in his Tardis, he forgets that Jackie is on board and takes a trip to Torchwood. Upon his arrival, he is greeted by a throng of soldiers and Yvonne - who knows his identity and that he doesn't usually travel alone. The Doctor brings Jackie out of the Tardis and introduces her as his companion, leaving Rose inside the ship to pursue her own covert plan of action.

Yvonne tells the Doctor - now a prisoner - of Torchwood's history. After showing him various alien artefacts, she hopes he can help them to unlock the mystery of the sphere. The Timelord discovers that the sphere has travelled to Earth from a hellish space that exists between dimensions, and came through 'The Void'.

Rose explores the building, but her presence is soon discovered by Dr Singh, who alerts security. He asks his laboraty assistant Samuel to look after her. This pleases Rose a great deal, for Samuel is in fact Mickey - last seen in a parallel dimension.

The Doctor becomes increasingly desperate for Torchwood to call off the next planned 'ghost shift', but to no avail as Adeola and Gareth - now back at the office - are under some kind of mind control and won't shut down the programme. The Doctor intervenes and removes their earpieces, which kills them but he explains they were dead anyway. He locates the source of the signal being sent to the earpieces to the area under construction. To his horror, a group of Cybermen surround him and march him back to the control centre.

The Cybermen - now effectively in charge of Torchwood - reinstate the 'ghost shift' and millions of figures appear around the globe... only to reveal their true identity as Cybermen. At the same time, the sphere begins to open... and it's a force far deadlier than Cybermen lurking inside...