Midnight

The Doctor and Donna Noble spend some leisure time in a leisure complex that has been constructed on the crystalline planet Midnight, which orbits close enough to its sun that the X-tonic radiation exposure would vaporise any living thing to walk unprotected on its surface.

While Donna enjoys some rest and relaxation at a spa, The Doctor decides to take a four-hour shuttle bus ride to a famed Midnight attraction - The Sapphire Waterfall.

He is joined by the Cane family, Val and her husband Biff and their teenage son Jethro, Professor Hobbes, who is investigating the waterfall with his assistant Dee Dee Blasco, and a businesswoman, Sky Silvestry. They are all made welcome by a steward who calls herself 'The Hostess'.

Donna Relaxing

The trip starts smoothly despite the shuttle being rerouted to a new course and the irritating onboard entertainment system which The Doctor soon disables – much to the relief of all those on board – except for 'The Hostess'.

En route though the shuttle mysteriously comes to a stop. The Doctor checks with the shuttle's driver and mechanic and they confirm that there is nothing wrong with the vehicle and so they decide to call for a rescue vehicle. They briefly open the shutter to look outside. But when it starts to closes the mechanic believes he sees a shadow moving towards the bus.

Alternative Entertainment

After returning to the main cabin The Doctor informs the other passengers that help is on its way and then, impossibly, something begins banging on the exterior, copying the passengers when they knock back. The knocking moves around the shuttle, apparently making its way towards Sky Silvestry and dents the door she is standing by. The lights then temporarily fail and the shuttle is violently rocked. When the lights are restored, the seats near Sky have been ripped off the floor and she is cowering in the corner. An attempt to speak to the cabin crew reveals that their cabin has been ripped away, killing Joe and Claude.

Sky initially remains motionless, but The Doctor manages to persuade her into turning around. Attempts to get her to speak only cause her to repeat what she is told, making it clear that Sky is no longer in control.

What is this strange intelligence that has infested one of the passengers? Why is she repeating everything that is being said and what will happen when she starts to speak in exact unison with the passengers and then before anything is said?

'The Hostess'

The Doctor finds himself trapped and fighting a losing battle against a rising tide of panic and paranoia when he becomes, apparently possessed by Sky, and so the centre of the hostility, he finds himself nearly dragged out of the shuttle bus and into the deadly atmosphere.

Will The Doctor manage to convince the other passengers, and the hostess, that it is Sky who is still possessed, and that he is the only one that can save them? Or will one of them realise what is happening and come to his, and the remaining passengers, rescue?