Where it all begins

A father is explaining to his small son how much money he costs him when he comes to stay for the weekend - it's £15 for the train ticket, and he has to make two journeys, and then there's the food, and the presents... Later on the little boy says that he's thinking about saving up the £20 his father has given him to buy a light sabre. He doesn't say what he'd be saving up for.