The Railway Children

A level 3 Oxford Bookworms Library graded reader. Retold for Learners of English by John Escott.
'We have to leave our house in London,' Mother said to the children. 'We're going to live in the country, in a little house near a railway line.'
And so begins a new life for Roberta, Peter, and Phyllis. They become the railway children – they know all the trains, Perks the station porter is their best friend, and they have many adventures on the railway line.
But why has their father had to go away? Where is he, and will he ever come back?