King Henry and his chancellor (and best friend), Thomas Becket, run the country well together
Henry makes Becket Archbishop of Canterbury and, as he is now the most important man in the Church, Becket becomes very religious
Henry doesn't like the fact that Becket now has his own ideas (eg. being religious and wanting clergy to be trialed in the Church Court instead of the King's Court) and so Becket runs away to France to escape Henry wrath
Becket returns after 6 years and he and the king make up... until Becket banishes all the priests who sided with Henry instead of him from England
Even angrier than before, Henry interrupts dinner one night to shout, "Will someone rid me of the troublesome priest?" to which 4 of his knights assume means, "Kill Becket!