An astonishing story of human kindness, self-learning, incredible pain, unbelievable hope and the sheer power of love to change a life.

Christmas 1975 and Queen's 'Bohemian Rhapsody' is riding high in the charts. In a residential street just outside Cardiff, a persistent knocking breaks the stillness of the evening ...

When Rob Parsons, a young lawyer, opens his door he finds a man standing before him clutching a bag of belongings and a frozen chicken. Rob and his wife, Dianne, invite him into their home, cook his chicken and offer him shelter for the night. What happens next is an astonishing story of human kindness, self-learning, incredible pain, unbelievable hope and the sheer power of love to change a life.

A Knock at the Door is the true story of Ronnie Lockwood, a homeless man who entered the home of a young couple, became a dustman and lived as part of their family for over 45 years until his death. But this is not just Ronnie's story - it is also that of Rob and his family. Outwardly the two men's lives were worlds apart - as Ronnie emptied rubbish bins, Rob flew on Concorde - and yet, they discovered they had similar struggles. Then the day came, at the lowest moment of the couple's lives, when they turned to the homeless man for help.

But there were also remarkable turnarounds. Ronnie spent much of his spare time volunteering, including at a homeless centre, and ended up having a 1.6 million well-being centre named after him. Rob left his law practice and he and Dianne began a charity that touches the lives of millions of people.

You will have never read a story like this before, but at its heart is a simple message: whether we are a lawyer or a dustman - tomorrow doesn't always have to be like yesterday.