Weeping Angels - Can be sent back

‘Which is why,’ announced the Doctor, finishing his breakfast, ‘which is why we have to take you home, Mark Whitaker.’

‘But if the Angels want a paradox,’ said Amy. ‘Why go to all the trouble of bringing Mark here? Why not just change history themselves?’

‘Because that would make them part of the paradox, they’d end up feeding on their own timelines. They need someone to do their dirty work for them. That way, they remain outside the chain of cause and effect.’

‘What if I can’t go back?’ said Mark.

The Doctor wiped his lips with a napkin and leaned forward. ‘What do you mean, “can’t”?’

The supermarket bustled with Sunday shoppers, mothers with pushchairs and fathers with trolleys. None of them paid and attention to the blue police box parked beside the Fireman Sam ride. But Mark couldn’t take his eyes off it.

It was the same police box he’d seen flying through the air after his train. The Doctor’s time machine.

‘Let me get this straight,’ said the Doctor, leaning proprietorially against the door. ‘You received a letter sent from your future self?’

Mark nodded. ‘I received it the day I travelled back, just before I met you, and the Angel.’

‘How do you know the letter came from you?’ asked Amy.

‘Because my name was at the bottom.’

‘Oh.’

‘And it was in my handwriting.’

***

Touched by an Angel, Chapter 6