But in the end, for all that work, Bardet lost four seconds to Froome and six to Cannondale-Drapac’s Rigoberto Uran, who finished third and second on the stage, respectively, to gain time bonuses. Uran is now level on time with Bardet at 27 seconds behind Froome, and in second overall, courtesy of his higher-place stage finish than the Frenchman.

Tomorrow, it’s possible we could see Ag2r shift tactics to something a bit closer to what they tried on the Peyragudes stage, which has some broad similarities to Stage 18. As then, the main difficulties in Thursday’s route don’t start until past the halfway point, so there’s less reason to be aggressive in the early break. Perhaps better to mark Sky and cover moves from them (say, an attempt to get Mikel Nieve up the road), and force them to control the gap to the eventual breakaway.

The difference is what happens on the first big climb. On Stage 12, Team Sky controlled the pace over the Col de Menté and Port des Bales, while all the other contenders seemed content to wait for the Peyragudes finish. Instead, what we might see on Stage 18 is Ag3r hitting the front on the first main climb of the day, the Category 1 Col de Vars.

The early part of the climb is not steep, but the final five kilometres ramp up more. Sky will want to control the pace, but not set it so high that they burn off too many of their own riders. You won’t see Bardet at the front, but if his Ag2r teammates like Matthias Frank and Cyril Gautier push the pace there, it could jettison Sky pacemakers like Sergio Henao and Mikel Nieve, leaving Froome with just Kwiatkowski and Landa for support. A hard pace on the descent might keep the stragglers from catching back on again before the final ascent, the Hors Categorie Col d’Izoard.

The question is: how badly does Froome need to be struggling for Landa to decide, on his own and possibly in contravention of team orders, that he has to leave Froome behind?

Based on what we’ve seen so far, Bardet can at most hope to whittle the group to about 10-15 select riders on the Izoard. Hopefully he’ll have Alexis Vuillermoz with him at that point to match against Landa. The early part of the Izoard will likely be just pacemaking—high enough to prevent others from re-catching but still conservative.

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The key part of the climb is the final seven kilometres, which is sustained and steep at more than nine per cent average. Expect Bardet to attack short of the Col de la Plåtrière. He will try to force a gap to Froome at that false summit, following which is a short downhill in the Casse Déserte, a barren and windswept section before the final, 2km-long, uphill kick to the line.

This is likely where Uran will try his luck as well. His Cannondale-Drapac team isn’t as strong in the mountains as either Sky or Ag2r. They may put a rider in the break, but they can’t control the race like either of the other two teams. So far, Uran has been quiet and opportunistic, riding a technically perfect race in following other attacks, but never making one of his own.

Where Bardet has shown his teeth, the question remains for Uran: has he been hanging on, or waiting to show his own strength? On Stage 17, Bardet’s aggression was matched only by Dan Martin’s, which backfired on Martin a bit when he was gapped over the summit of the Galibier and ended up losing a further 20 seconds to the lead trio.

Cracking Froome may well rely on an alliance of sorts, with Bardet and Uran trading attacks along with Fabio Aru, who dropped from second to fourth overall on Stage 17 and will want to climb his way back up on the podium. (A stage win is a possibility for Aru; the overall victory is probably done for him.)

The question for Chris Froome is twofold: how well can he respond to attacks from the others, and how much can he depend on Landa to help? The answers are intertwined. Froome’s only real moment of difficulty this Tour was the Peyragudes finish, where he was uncharacteristically dropped in the final moments. Froome hasn’t had the kind of climbing kick he’s shown in past Tours, but neither have the others been able to distance him much.

The Izoard, however, is a unique creature. The summit is 2,360 metres—slightly below the race’s high point Wednesday of the 2,642-metre Galibier and quite high by Tour summit finish standards. So altitude can play a role, as can winds in exposed sections if Froome’s isolated. And, while the riders have done the Izoard before, it has never in race history been a summit finish. That’s a different dynamic entirely than going over the top knowing you have 15km of descent to Briançon to make up time.

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Landa might be the key. He is arguably the strongest rider in the race but will be expected to work for Froome. If Froome experiences some historic crack and is dropped decisively on the Izoard, then Sky might set Landa free to race his own race. But that’s unlikely, so the question is: how badly does Froome need to be struggling for Landa to decide, on his own and possibly in contravention of team orders, that he has to leave Froome behind?

Remember Froome’s time trial skills. He can probably afford to be as much as a minute behind Bardet going into Saturday’s TT and still pull out the overall victory. His comfort margin with Uran is smaller, maybe as little as 30 seconds. But in either case, he can probably afford to lose some time on the Izoard. Even if Froome is dropped, he will not panic (because he pretty much never does), and so Landa will likely stay with him to make pace.

So, the more likely possibilities are these:

• Ag2r rips the race open and Bardet surges to solo victory and yellow.
• Or, Uran follows wheels and launches his attack at the perfect moment to ride away and into yellow.
• Or, Chris Froome doggedly repels all attacks and stays in yellow.
• Or, Froome cracks and Landa attacks.
• Or, finally, Froome manages one final offensive and drops the others and puts the 2017 Tour firmly out of reach.

With the top three riders within 27 seconds, a fourth another 26 seconds behind and the strongest rider in the race hovering at 1:24 from the lead, almost anything can happen. There is still the Provence stage and the time trial. But the 2017 Tour may well be decided on the slopes of the Izoard.