What to Do About Holly by Joan Lingard 

'Come on Holly,' said her mother, grabbing her free hand.  'And stop dragging yer fee or you'll miss yer train.'

'I'm not wantin' to go on the train on my own.'

'Well, you'll have to, won't you?  I can't take you, I've my work to go to.'

When Holly's mother puts her on the Edinburgh train, in the care of a complete stranger, who happens to be a children's author, none of them have any idea of what is going to happen.