Tilly is going to stay with her gran and great-gran in Wales.
She's got a big school project about the Second World War to do and Gran, who was evacuated herself during the war, has promised to help.
Travelling on the train for the first time alone, Tilly falls asleep and wakes up to discover she's travelled all the way back to World War II.
She's being evacuated to Wales with her two younger brothers.
Stern Mr Edwards offers to give them a home on his remote farm, where she meets a very special sheepdog.