Arthur, whose mind, in the mean while, had been poisoned by officious courtiers, besieged his recreant wife and knight; but although repeatedly challenged, the loyal Lancelot ever refused to bear arms directly against his king.
When the Pope heard of the dissension in England he finally interfered; and Lancelot, assured that Guinevere would henceforth be treated with all due respect, surrendered her to the king and retreated to his paternal estate in Brittany.

As Arthur's resentment against Lancelot had not yet cooled, he left Guinevere under the care and protection of Mordred, his nephew,--some versions say his son,--and then, at the head of a large force, departed for Brittany.
[Sidenote: Treachery of Mordred.] Mordred the traitor immediately took advantage of his uncle's absence to lay claim to the throne; and loudly declaring that Arthur had been slain, he tried to force Guinevere to marry him.

As she demurred, he kept her a close prisoner, and set her free only when she pretended to agree with his wishes, and asked permission to go to London to buy wedding finery.
When Guinevere arrived in that city she intrenched herself in the Tower, and sent word to her husband of her perilous position.

Without any delay Arthur abandoned the siege of Lancelot's stronghold, and, crossing the channel, encountered Mordred's army near Dover.
Negotiations now took place, and it was finally agreed that Arthur and a certain number of knights should meet Mordred with an equal number, and discuss the terms of peace.

It had been strictly enjoined on both parties that no weapon should be drawn, and all would have gone well had not an adder been lurking in the grass.