Imagine Shakespeare wrote a tragedy about King Arthur. What would it be like?
Note that he wrote about a hundred years after Malory, so that would be the "chronicle" he'd adapt into the play. Of course, Malory's long book would need to be drastically abridged; Shakespeare would take the main themes and pick and choose (and innovate) his subplots based on his personal preferences and political themes. Let's forget the Saxons, just like Malory forgets them; the main foreign foe would be "Lucius Dictator of Rome." In Shakespeare's time, I think everyone would more or less see that as a reference to the Pope, the current political enemy and Antichrist seated at Rome. So... let's have Arthur's foe be the Pope. With Shakespeare's usual disregard for history, let's have Pope Lucius be ruling the Western Roman Empire including France, thus bringing him in easy range of Arthur.
In a tragedy, the main character of the tragedy is brought down by some tragic flaw. For a Shakespearean audience to accept a flaw in Arthur, it needs to be a virtue taken to extremes. Given how both Lancelot and Mordred are knights in Arthur's court, and given how he believes in Guinevere's virtue until indisputable evidence is brought to him, I believe a good tragic flaw to attribute to Arthur would be over-trusting.
Next, for the domestic enemies: The main domestic enemies in Malory are Lancelot, Mordred, and Morgan le Fay. Lancelot is associated with France (not so in Malory, but let's say Shakespeare gets word of this association), so let's start the plot...
* In the first scene, Sir Lancelot arrives in Arthur's court and hears various knights talking about Arthur's valient exploits. In a soliloque, we learn that Lancelot has been sent by the Pope to spy on Arthur, and he's currently looking to gain a network.
* In the second scene, Arthur makes an obviously wise ruling in some case. Lancelot in an aside recognizes Arthur's wisdom and wonders whether he'll see through him. However, Arthur receives Lancelot politely and takes his story on faith. We also learn that Arthur and his court don't think much of France, which is still ruled by the Pope.
* In the third scene, Sir Kay the pompous seneschal (read Polonius from Hamlet) rebukes... let's say Sir Dinadan (read one of the sailors from Tempest) and Sir Lamorak (perhaps read Edmund from King Lear?)... for their rude behavior. We note both of them speak in prose: they're Shakespearean clowns. As they're wondering what to do, Lancelot comes up and recruits them to pass him information. They immediately run off to listen in corridors. Lancelot sighs and soliloquizes that it's a start, anyway.
* No later than the start of the second act, the Pope of Rome sends a letter ordering Arthur to submit to his spiritual overlordship, in terms from an Elizabethan's worst nightmares. With the unanimous consent of the court (even Lancelot agrees in word), Arthur rejects it and declares that Christianity in Britain owes nothing to Rome but comes straight from Joseph of Arimathea. (Read the consultation over the Salic Law at the beginning of Henry V.) Arthur sends back a rejection and orders his knights to search for the Holy Grail, which will confirm that Joseph of Arimathea did indeed evangelize Britain independently from Rome. (Okay, Shakespeare was never a historian.)
After several adventures and antics of clowns, Lancelot sees the Holy Grail and soliloquizes that he almost wishes to bring it back, though it would tear apart all the plans of his master the Pope. The Pope would obviously wish for him to destroy it... but he can't! Instead, he leaves it alone.
Either just then or later, Sir Percival comes in and finds the Grail and brings it back. Arthur orders a lavish cathedral built to house it. Lancelot is now satisfied, and he declares that he's now loyal to Arthur... but just then, the clowns enter with more trivial spy information! Lancelot has to promise to write it up anyway. From this point on, he's playing a double game.
Eventually, Lancelot runs for France (probably summoned by his ostensible master the Pope) as Arthur prepares for war with the Pope. I don't know exactly how to get there, yet. Where are Mordred and Morgan going to enter in? I'm pretty sure Mordred will be played as Iago from Othello... but I'm not sure whether he's working for the Pope, for himself, or pretending to work for the Pope but actually for himself. Nor do I know when or how he'll get involved with the Lancelot plot. One way or another, though, Mordred gets Guinevere to go to France with Lancelot - which immediately forces Arthur to launch his war efforts half-cocked so as to get her back.
Then, of course, Mordred seizes power, Lancelot is killed thanks to Mordred, and Arthur is all but slain at Camlann.
Thoughts?
Suggestions for the middle of the play, or other characters, or how Mordred and Lancelot's plots will work together, as my offline friends and I keep developing this?