All the striving, all the high ideals, have come to this: a test of exquisite complexity in a place where even the grandest dreamers can be destroyed. A test of everything Arsenal want to be.
When Andrey Arshavin scooted across north-London turf to give Arsène Wenger's team a 2-1 lead in their Champions League duet with Barcelona, he twisted all normal thinking. Arsenal parade a pioneering spirit but in this rematch they are required to hold what they have. Instead of elaboration all the talk is of elaborate strategies.
This is not the modern Arsenal way. When these two versions of a single idea reconvene in the Camp Nou the English representatives will be bounced into a game of fight or flight, attack and retreat, in which the capacity to make the correct tactical decisions in an inferno of psychological pressure will matter as much as stylish passing. Any player who thrives under such duress need never doubt himself.
The London game vindicated Wenger's faith not in kaleidoscopic movement so much as vengeful counterattacking: a policy that will be much harder to go with in the probable absence of Robin van Persie, their best finisher, and Theo Walcott, the team's quickest and most direct runner. Nor is the rushing back of Cesc Fábregas from injury conducive to a smooth application of Arsenal's biggest strengths.
First time round a break-out strategy rescued the good from the even better. It halted Barça's ball-hogging and sent Arsenal's supporters into the night exultant. Their heroes recovered from 1-0 down at the interval by invading the space behind Barcelona's defenders, who press high up the pitch and assume the victim will be too dumbstruck or slow to exploit the unmanned space.
Can this work again in a stadium where Barcelona have won 18 of their 21 home fixtures and where Lionel Messi scored four against the Gunners last year as retaliation for Nicklas Bendtner's impertinent early goal? Arshavin's raid three weeks ago worked as an epiphany but also as a provocation. It was the instance of defiance that guaranteed Barcelona would be at their most eager and inventive when the clubs met again to settle the argument.
The twisting of mental ropes is therefore more audible in the Arsenal camp than that of Barcelona, who will feel sure they can progress if they convert the kind of chances they squandered at the Emirates or if they simply replicate their best league form. Then a 1-0 win would suffice, on the away goals rule. Arsenal on the other hand must bend their own identity and switch between attacking and defensive modes as circumstances require.
To inflict death by endless passing is Wenger's creed but there is no scope for it in Catalonia, except when Arsenal recover the ball and attempt to strike back hard and fast. "We will have to play another way, because it's one of the few games where we will spend 60% of the time defending," Wenger says.
Haunting their supporters is the memory of a recent opportunity thrown away. The Carling Cup final was lost when Wojciech Szczesny (goalkeeper) and Laurent Koscielny (centre-back) contrived a penalty box farce which Birmingham City exploited to extend Wenger's six-year wait for a trophy. "We have to fight against the pre-conceived ideas, because the only way of thinking is that Arsenal cannot defend," Wenger protests. "I will just remind you that in the last 11 games we have seven clean sheets in the Premier League. We have conceded less goals than Man United, who have a very good defence. We can defend when we have to. We prefer to attack, that is for sure."
The suffocating intensity of this tie is Arsenal's punishment for losing at Shakhtar Donetsk and SC Braga in the group phase. A second-place finish might have pitted them against Real Madrid, Bayern Munich or Schalke. But the entertainment deities decreed they should face a superior version of themselves. All neutrals should give thanks for that.
Their overall record against Barcelona was inauspicious until last month's win broke a sequence of five encounters without a victory, yet there are spots of light. Arsenal were 2-0 down at home in last year's first leg but recovered to draw 2-2. This time they trailed to a David Villa goal before Van Persie and Arshavin flipped the plot. Only the 4-1 defeat at Camp Nou last April really hurts: "the Lionel Messi show", as Wenger remembers it now.
This is Arsenal's 13th Champions League campaign and the 11th consecutive time they have advanced beyond the group stage. Barcelona were insurmountable in the 2006 final as well but at least last month's win demonstrates the absence of an inferiority complex on Arsenal's part. Still elusive, though, is an explanation for their ability to lead 4-0 at Newcastle and draw 4-4, donate a goal at the end of a Carling Cup final but display no trace of fatalism while one-down to Barcelona, their nemesis.
"I know this team will become stronger and stronger," Wenger said again the other day. This is his theory of endless self-improvement, repeated endlessly. The trouble is: this is not a game solely of conundrums and tactics. Beyond plans and schemes an immense array of individual talent confronts Arsenal in Spain. They face not only an artistic manifesto but a mass of threats in single form. It could get Messi.