So, it's a last ditch Hail Mary effort, but Sam and Dean tromp off to England to find the Holy Grail; Castiel magicks them across the Atlantic, thus avoiding all those pesky questions by the authorities, who would, one imagines, be quite disturbed by the arsenal, metaphysical and mundane, that the boys feel obligated to haul around. (Not having the silver falchion the one time it would have been really, really useful made them even more paranoid about such matters.) While tromping about the bucolic English countryside, they helped themselves to the goods of the Collective, who were maybe beginning to think that ownership was a handy thing - it certainly have would made deciding who should risk the smite down from righteously upbraid the interlopers so much easier.
Amongst other adventures, Sam gets into a pub quiz with Sir Bedevere (Sam wins on the technicality of being able to walk out of the establishment), Dean burns down the shrubberies of the Knights Who Say Ni (who the hell as the time to put up with such nonsense, sayeth Sir Dean [the fire marshals weren't thrilled, but they could never *prove* it was arson instead of the new age hippies paying insufficient attention to their bonfires]), and Dean utterly fails to flirt with the Lady of the Lake (her raised eyebrow said it all, and Dean had a healthy respect for women who routinely handled sharp, pointy, magickal objects).
God, amused by their antics, challenges the boys to a poker game for possession of the Holy Grail (which he guarantees will solve their little Lucifer problem, or their money back [when Sam rightly brings up the question of what money, Dean shushes him - not out of respect, you understand, but because God can put the big smite down]). The Winchesters win, although they never do reveal who held the winning hand.