Forty years ago on 1 July, Wales was celebrating one of the great royal events of the 20th century - the investiture of the Prince of Wales at Caernarfon. It was a day of pomp and pageantry, but also a day of bombs and threats to the lives of the royal family. Presenter Huw Edwards chronicles the extraordinary events of a day when police, politicians, and royalty held their collective breath as a group of nationalist extremists violently plotted against the investiture.