So I promised you marvels last time, right? Check this out. First, the doors and windows of the hall all slam shut of their own accord! Second, it’s suddenly totally dark in the hall, even though there’s a wide assortment of torches and candles and lanterns all set up! All the knights start to freak out, because this is crazy!
Arthur rises to his feet, to calm the crowd. “Everyone, everyone, it’s going to be okay. This is just a strange adventure. We’ll get through this. I’m sure things are going to get stranger before they become less strange.”
Around this time someone points out the two men standing in the middle of the hall. No one saw them arrive; they’re just there, all of a sudden. The first man is a good old man, and an ancient, clothed all in white. I’d guess it was Merlin, except that Merlin’s been inside a magic cave since the start of Book IV. With him there’s a guy, and Malory tries to be coy about this reveal but screw that, it’s Galahad. He’s all in red, and has armor on but no sword, just an empty scabbard.
“Hello!” says Galahad, because everyone’s staring at him. He waves.
“Sire,” says the old man who isn’t Merlin, “allow me to introduce Sir Galahad, kin of both King Pellam and, going back far enough, Joseph of Aramathea. He comes now to accomplish all kinds of great mystic deeds.”
There’s a silence, while this sinks in.
“Huh,” says Arthur. “Nice to meet you, Galahad. Welcome to Camelot.”
Galahad steps forward to, I don’t know, shake Arthur’s hand or something, but the old guy who sure acts a lot like Merlin intervenes. He grabs Galahad by the shoulder and hisses at him to take his armor off and put on his nice new red ermine coat. Galahad doesn’t see why he has to change out of his armor so soon after putting it on, but he obliges the old man.
“It’ll have to do,” sniffs the old guy, who at this point I’m just going to accept is Merlin in a surprise cameo. Merlin snaps his fingers and points to the Siege Perilous, which as you may recall Kay put a slipcover over.
In response to Merlin’s signal, Launcelot lifts the slipcover up off the Siege Perilous. And whoa! The golden writing on it has changed! Now it says This is the siege of Galahad, the haut prince.
“There, you see?” Merlin barks at Galahad. “Your seat. Sit!”
Galahad sits. “Thanks, Merlin. You can go now. If you see King Pellam, tell him hi for me? Also say hi to Petchere.”
To answer your question, no, I don’t know who Petchere is, either.
And then Merlin leaves! The only casualties of his visit are twenty horsemen whom he drafts to escort him back to wherever he’s going, which fellows are never seen or heard from again apparently. Everyone breathes a sigh of relief, because thank God Merlin is gone.