"Siege Perilous" is the third episode of the fifth season of the American fantasy drama series Once Upon a Time, which aired on October 11, 2015.
While the residents of Storybrooke attempt to work on finding a way to free Merlin, Arthur shows up when David comes across an item in a book.
As they reach a bridge that can only be used by one person, David volunteers to take the challenge and snatch the toadstool, but as he attempts to return he is obstructed by phantom knights that drag him underwater.
However, later that evening, Mary Margaret comes across a very much alive Lancelot, who warns her that the Dark One isn't the only villain in Camelot - it's King Arthur.
The insinuation is corroborated, as Guinevere joins Arthur at the Round Table, he takes out the toadstool that was supposedly lost to add to the reliquary, which holds the magic relics collected by the knights.
While it brought Arthur no pleasure to lie to someone he sees as a good and noble man, he tells Guinevere that he must think of his kingdom first.
David gives Arthur a crash course lesson in driving as he takes a piece of wood, using it as a makeshift joust, and knocks Grif off his horse.
However, there was no magic bean found among the stolen items, but at the camp, David recognized the Crimson Crown on the ground and took it to Regina, who had also seen the question mark that she had handwritten on its illustration back in Camelot.
The pickaxe breaks, and Rumplestiltskin's manifestation appears, telling Emma she needs a true hero in order to pull out the stone.
I had Arthur pegged as sketchy the moment he seemed to be okay with Charming going over the water by himself, but I should’ve started side-eyeing him when he gleefully suggested that Guinevere and Snow should be pitted against each other.
"[2] Amy Ratcliffe of IGN said of the episode, "Tonight's Once put some important pawns into place with Arthur's villainy (and Lancelot) and Gold's return to the world.
[3] In a review from Rickey.org, Nick Roman said, "“Siege Perilous” is certainly as good a starting point as any for Once Upon A Time to once again explore what makes a hero.