So Boomerang was directly responsible for the fall of Camelot. Yeah, I can see that.

I'm not deeply versed in the legends of King Arthur, in less you count having seen Excalibur like forty times, but we've seen a few versions of Camelot here over the years: Iron Man and Dr. Doom's classic visit, DC's Camelot 3000 style, the Black Knight or the Demon. About the only common thread between them is there once was a Camelot, and it fell. Same with today's book! From 2012, Thunderbolts #170, "Days of Lore" Written by Jeff Parker, pencils by Kev Walker, inks by Terry Pallot.

This version of the Thunderbolts had been criminals in a rehabilitation program (reminiscent of Suicide Squad, although somewhat more humane) but had escaped through time with their tower. Currently at Camelot, the entire roster has been thrown into the dungeons, except for Ghost, who had been observing the team for some time. Ghost frees them, even as the assorted trolls and monsters imprisoned there beg for their freedom. Moonstone figures they can fly over to Thunderbolts Tower and escape (probably back to cavemen times, but at least away from Merlin) except several things are happening at once: the Black Knight went to the dungeon to confront Boomerang over their previous fight, and discovered they were gone. Merlin and Arthur were trying to get into Thunderbolts Tower, possibly by cutting into its engines with Excalibur, and Guinevere and Lancelot are, um, taking advantage of those other distractions.

The escape isn't going well, until the arrival of the monsters Boomerang freed from the dungeons; who seem a helluva lot less sympathetic when they're calling themselves the Son of Beowulf and tearing up the place. Before the team gets to the tower, Merlin confronts them, not to stop them, but to tell them how they've just doomed Camelot. Merlin knew the knights were becoming obsessed with the quest for the Grail, even though that probably wasn't the defense needed against Morgana le Fey and Modred. Merlin convinced the knights to capture the monsters and put them in the dungeons, since he knew Morgana and Modred would open the dungeons for allies, and then get immediately killed. Since the monsters were now being killed, Boomerang just blew that plan out of the water.

The Thunderbolts head on to the future, but don't quite get to the present; while Merlin has to pretend everything's peachy in Camelot to his king. Depressing life, being Merlin. Nothing but spoilers, I figure.