Peter, Roberta and Phyllis' lives change overnight when suddenly Father is taken away by two strangers.
They move from the comfort of their London residence to a modest country cottage, and find that Mother is no longer able to entertain them as she must write slavishly to support the family.
Once fairly wealthy, they are now 'poor' and must adapt accordingly. But with this change comes more freedom than they could ever have dreamt of, as they learn to entertain themselves and forge their own moral code. So begins a tale of blissful independence and adventures aplenty with the railway line at the bottom of their garden becoming central to the children's lives. Not only do the railway line, its station and staff offer the trio a world of new friendships - with pride of place going to Perks, the porter - it also introduces them to the man who will help right the terrible wrong that blights their life.