Read the full text of King John with a side-by-side translation HERE.
King John is chillaxing on the English throne when a messenger from King Philip of France shows up and declares that John's claim to the throne is totally bogus. King Philip wants him to hand over the crown ASAP to John's young nephew, Arthur, who (probably) should have become king when Richard I died.
King John is all, "Fat chance. I'm the rightful king. Prepare for war." He sends the French messenger packing. King John slaps his army together and sails to France for a big showdown with King Philip's forces outside the walls of Angers. The two kings try to negotiate but get nowhere fast, so the English and French armies go to war. The battle is a draw. Finally, the citizens of Angers come up with a better plan—King John's niece Blanche should marry King Philip's son Louis, creating an alliance between the two kingdoms. Yay. Problem solved.
Just after Blanche and Louis exchange vows and smash wedding cake into each other's faces, Cardinal Pandolf shows up on a mission from the Pope. The Pope is all mad because King John won't do what he's told. John is all "I'm the King of England—the Pope doesn't get to tell me what to do." In response, Pandolf announces that 1) John is banned from the Church, and 2) the Church will give special props to anyone who takes him out.
Then Pandolf orders King Philip to stop being friends and political allies with King John... or else. King Philip obeys, and France and England go to war... again. This time, the English army takes little Arthur prisoner. Before they sail back to England, King John tells Hubert (his loyal henchman) that he wants the little brat dead, PRONTO.
The scene shifts back to England, to the castle where poor Arthur is being held prisoner. It turns out that Hubert is actually supposed to burn out the kid's eyes with hot iron pokers. But Hubert and Arthur have become chummy, so Hubert lets him live and tells him to lay low for a while so John won't find out. When the English noblemen hear the "news" that Arthur is dead, they get all mad at King John for being a kid-killer and storm off to find the boy's grave.
At this point, John gets some bad news: Louis, the Prince of France, is totally invading England. John starts freaking out until Hubert reveals that Arthur isn't actually dead. John is pretty overjoyed to hear that. He sends Hubert and the Bastard to find the nobles and tell them. Unfortunately, at that very moment, Arthur jumps off the wall of the tower and dies while trying to escape. The noblemen find his body and think he's been murdered by one of King John's henchmen. In their outrage, they decide to rebel and join forces with the French invaders. Now John has the following people ticked off at him: the Pope, his noblemen, and France. This is not good.
In a tight spot, King John swears loyalty to the Pope because he wants the Church to have his back. As payback, Pandolf tells Louis to back down, but Louis refuses and proceeds to invade England. King John's forces go toe-to-toe with the French army and the English rebels, but nobody is really winning. Then, out of nowhere, King John starts feeling a little sick and leaves the battlefield to rest. Meanwhile, when the English rebels find out that Louis plans to betray them if he wins, they ditch him and join up with King John again.
Good news, right? Not so fast, Shmoopers. It now turns out that King John has been... poisoned... by a treacherous monk. Gasp, right? (And, yes, that's totally random, just like a lot of other things that have gone down in this play.) John up and dies on us, leaving the throne of England to his son Henry (a.k.a. King Henry III). Prince Louis takes his army and heads home for France, supposedly because Pandolf has cut a deal with him.
England is safe from a foreign threat… for now.