New plot
I am ripping off Star Trek (mostly) for this plot. As the Guardian says, the TARDIS will be landing on a spaceship under attack. You can find nearly anything you like here, including bit not limited to: some decks having oxygen, others with gravity, some rooms will be open to the elements. It will be dark and creepy, wherever you are.
There is the odd crew member still alive and hanging around. They won't behave suspiciously at all. At first. The trouble is that an alien being has got into the ship and is taking over crew members. Said alien being can transfer to other living beings by touch. Once they're gone from someone, that person won't remember anything that happened while they were being possessed.
What the alien wants is to go home and is prepared to go to any length to get it. Just to make matters worse, it's capable of taking over the TARDIS too...
There is the odd crew member still alive and hanging around. They won't behave suspiciously at all. At first. The trouble is that an alien being has got into the ship and is taking over crew members. Said alien being can transfer to other living beings by touch. Once they're gone from someone, that person won't remember anything that happened while they were being possessed.
What the alien wants is to go home and is prepared to go to any length to get it. Just to make matters worse, it's capable of taking over the TARDIS too...