I was so sure this had been made into a movie (starring Walter Pigeon, I was guessing) back in the 50s, but no. apparently not. But it has such an odd plot structure I suspect Costain had his hopes.
So we have elderly retired Senator Richard O’Rawn, Lion of the West, summoning young John Foraday to his vast Wyoming ranch on mysterious business. John is a promising writer, and apparently indirectly connected with the Senator. Turns out the Senator wants to take him to England to visit various historical sites, especially Castle O’Rawn, near Runnymede. Here the Senator, who has never been here before, directs a dig under a floor in the castle which reveals an underground vault in which lies a wooden box containing a crumbling copy of the Magna Carta and a few coins, which O’Rawn specifies before the box is opened. How does he know? Flashback! We are now back in the England of bad King John, and the Plantagenets, a temperamental crew.
The main portion of the book now begins, which is a straight forward historical fiction. Turns out Costain is somewhat of a Plantagenet expert, so he gives a vivid account of the convoluted goings on of this era in British history, as well as keeping you guessing who the original O’Rawn is. I must admit to having been a total fangirl of Costain back in the day, when I first started to read Grown Up Books. But I still think the framing device on this one is weird.