Closed book

Her courteous, sedate, inexorable husband, whose will she could not bend, whom she could not cajole, whose mind was a closed book to her — a book which had lain by her hand for three years, which she had never had the curiosity to open!

Like the activities of British Railways Research Department, developing, testing and modifying diesel locomotives before their acceptance for service is another behind-the-scenes activity which is a closed book to most passengers and to many railwaymen.