It's time for some exposition to advance the plot, so listen up!
After fifteen years of not seeing his brothers, Gareth has shown up in Arthur's court. No one knows who he is, so Sir Kay makes him work in the kitchens.
Lancelot has treated him kindly, though, and sees to Gareth's chivalric education. He even knights him.
Even the youngest of the Orkney boys, Mordred, has come to Arthur's court. Morgause doesn't like this one bit—she's now lost all of her sons to the King.
From the get-go, Lancelot did not like Mordred; even though he has no idea Mordred is Arthur's son by Morgause (this has been kept secret at court—not even Guenever knows about it). The guy's just that unlikable.
Morgause, it turns out, has become quite the cougar. She's got her claws in Sir Lamorak, King Pellinore's son, even though she's old enough to be his grandma. He's shacked up in Orkney right now.
Arthur knows this is not good news: Pellinore killed King Lot, and Gawain killed Pellinore.
Suddenly, Arthur wants to know where Gawain, Mordred, and Agravaine are.
The King recognizes that the whole Round Table idea was a huge mistake. He wanted to get rid of Might being used for bad, but the Round Table itself was founded by force.
Gareth enters, and gets a message. He announces his mother is dead—Agravaine has killed her.
It gets worse (although what can really get worse than killing your own mom in her bed?). Gawain, Agravaine, and Mordred have hunted down Sir Lamorak and killed him in an unchivalrous manner: they surrounded him and Mordred stabs him in the back.