The English Civil War much like our own in America has been fodder for numerous historical adventure stories. And the stories have been told from both the Cavalier and Roundhead sides with each taking turn at being the hero and villain of same. It was that kind of period in the United Kingdom history, subject to many different interpretations on all sides.
In this one the Royalist cavaliers are the heroes, they've been driven underground pretty much in 1648 and are now concerned with rescuing King Charles I and spiriting him away to safe exile. Charles is now in the custody of Colonel Lionel Jeffries and Captain Oliver Reed of Oliver Cromwell's Ironsides army and is on the way to London for trial and execution.
Jeffries has set up headquarters in the manor of the Beverleys who were Royalists now dispossessed of their property. Jeffries is one real pig as I recall and not living the spartan puritan life that his kind were wont to preach about. He's even got a marriage arranged for his daughter June Thorburn to Oliver Reed. But June's a secret Royalist whose heart is set on Jack Hedley the elder of the two Beverley brothers who is leader of an underground group of Royalists.
The intrigue in trying to rescue the King is tangled up with the romantic intrigue of this triangle and it leads to a lot of tragedy all around. History tells us what happened to Charles I, if he ruled rather badly, he certainly died nobly for his cause. As for the personal intrigues, you have to see the film for that.
The Scarlet Blade was playing as the second half of a double bill as I recall, probably with some Hammer horror feature. I remember at the time thinking how much more interesting Oliver Reed was as the shrewd, but villainous Roundhead than Jack Hedley was as the dashing, but rather wooden cavalier. Maybe Thorburn ought to rethink what she's doing. Of course this was before Oliver Reed became an international star, but his appeal was dead-on.
If you get a chance to see The Scarlet Blade, you'll see an average, but entertaining swashbuckler that might have been better with Reed as the hero.