The Railway Children
Bobby, Peter and Phyllis live in a lovely house in a posh bit of London. Then one day their father is taken away to prison uner suspicion of treason. The children are not told why. The house is sold, the servants dispersed and with their mother the children go to live in a tiny cottage in the country. Every day the children go down to the railway line and wave at the passing train, and every day an old gentleman waves back. Bobby decides they should write to the gentleman on the train and ask him to help get their father back. Time passes but nothing seems to happen, until one day father returns. And the children learn that it was the gentleman from the train that had helped secure his release.
