This bit here is pretty famous: Elaine of Astolat, aka the Lady of Shalott comes down the river in her funeral barge, where the knights of Camelot find her.  Alfred, Lord Tennyson, wrote a poem you might remember from Anne of Green Gables:

“Who is this? And what is here?”

And in the lighted palace near

Died the sound of royal cheer;

And they crossed themselves for fear,

All the Knights at Camelot;

But Lancelot mused a little space

He said, “She has a lovely face;

God in His mercy lend her grace,

The Lady of Shalott.”

Anyway.  Arthur and Guenever are the ones who spot the barge first, from out a high window at Camelot.  At first they can’t figure out what it is; it looks like a boat, but there doesn’t seem to be anyone moving around on it.  Arthur calls over Sir Kay, and points it out to him.

“Any ideas?”

Kay squints at it and shrugs.

“Go down with, uh, him and him.”  Arthur points to the two closest knights on hand, Sir Agravaine and Sir Brandiles.  “And bring me ready word what is there.  No, actually, I’m coming, too, because Malory says that four knights go to investigate.”

So Arthur, Kay, Brandiles, and Agravaine head down to the water, where they rope in the boat and climb aboard.  Inside, of course, they find the fairest corpse lying in a rich bed, and also the boat’s pilot because Malory can’t make his mind up about whether there was a pilot.  If there’s a pilot then no word would he speak, because that would defeat the whole purpose of the royal letter.

So the four knights go back to Arthur and Guenever, and in a stunning continuity error Arthur tells himself about Elaine’s exquisite corpse.  “That fair corpse will I see,” declares Arthur.  He goes back down to the water again, this time leading along Guenever.

Arthur, Guenever, and certain knights — Malory isn’t about to commit to a particular number, like three or four, it’s enough to know that only certain knights came with — board the barge, and examine Elaine’s corpse.  She’s covered in riches and finery.

Guenever spots the letter and points it out to Arthur, who picks it up and carries it back up to Camelot.  Apparently King Arthur is illiterate, because he calls for a clerk to read it.

“Dear Sir Launcelot,” reads the clerk.  “Now that I’m dead the question of how much sex we did or did not have will never be resolved.  My official position is that I was your lover.  Please give me a nice funeral, and I would like you, Launcelot, to offer ye my mass-penny, which is something we do in these olden times.  Sincerely, the virgin (or was I?) Elaine of Astolat.”

“How odd,” says Arthur, while Guenever breaks down sobbing.  He calls for Sir Launcelot, who has been conspicuously absent, and has the letter read again.

“I did not murder her,” is the first thing Launcelot says once he’s heard the letter.

“I wasn’t accusing you of anything,” says Arthur.

“Good.  Just so we’re clear.  I’m sorry she’s dead and I didn’t murder her and Sir Lavaine here will attest to that fact.”  Launcelot waves in Sir Lavaine, who agrees that Launcelot did not murder Elaine.

“You might have been nicer to her,” Guenever sniffs.

“Well…” Launcelot seems at a loss for words.  “She wanted to marry me, or to be my mistress on the side, and I said no, and then I totally offered her a lot of money…”

“I don’t remember that part,” mutters Lavaine.

“A thousand pound yearly to her and to her heirs,” lies Launcelot.  “All she had to do was marry someone else, anyone else.  I didn’t want to marry her!  I didn’t love her.”

“It’s true,” says Arthur.  “The heart wants what it wants.  Many knight’s love is free in himself, and never will be bounden.  But there is the matter of this letter.  I assign you the Quest of Elaine’s Funeral, Launcelot.”

So Launcelot arranges a lavish funeral for Elaine, and offer[s] her mass-penny.  Afterwards Guenever calls in Launcelot and chews him out royally for the whole big mess, and Launcelot tries to defend himself but doesn’t have much of a leg to stand on.

The end!  No moral.

PS Sir Lavaine spends that winter showing everyone in Camelot how great at venery he is.