What is the theme in A Place Called Freedom by Ken Follett?

The dominant theme of the book is the desire for freedom and happiness. The Scottish coal miners live a harsh life of misery at subsistence wages. They are basically the property of the mine owner if they work a year and a day past their twenty-first birthday. If they try to run they are captured and returned to the owner and an iron collar is placed around their neck. This is the kind of life that Mack McAsh escaped from, with the help of Lizzie Hallim. He goes to London where he enjoys the freedom he has to come and go and do what he wants.