The Polka-dot jersey is for the best climber, and it's allocated based on points for the first rider over various hills, passes, and mountains. Mostly it's decided in the second week of the race when the riders visit the Alps and the Pyrenees, but to keep the race interesting there are also points on offer for smaller rises at the beginning and end of the race. Sometimes the climbing classification has been close enough for the few points for a small hill on the last day can make the difference. And having some points at the beginning of the ride gives some more incentive for sprints and especially breakaways in the first week. Often the first couple of days don't have any points at all, though, because you do have to come up with something tall enough to be worth calling a hill. There aren't any hills tomorrow, and there's only one on Tuesday's stage, but there were three today, and that's what Millar decided he was going to chase.
Here's the thing, though. Millar does not have enough endurance to do an all-day breakaway, either by himself or in a small group. He's not enough of a sprinter to be assured of climbing points if someone else is with him, which compounds this problem: in order to get points the breakaway has to be solo and therefore more energy-consuming. And riders in long breakaways that get caught often have trouble keeping up with the group after they get caught because they're so tired. So what's Millar's strategy today? Ideally, he'd break away in the first half of the race, get enough points in the first two hills (which are relatively close together) to be assured of the polka-dot jersey and could then let himself get caught by the pack and ride the rest of the way to Canterbury, perhaps contesting points on the third hill if there were no breakaway there. This is what he did, and when four people followed him in the breakaway he did not wait for them to take advantage of sharing the work until after the first climbing points. Finding himself in a group breakaway he decided to try to outsprint his companions in the second climb, but it's not surprising that he wasn't able to beat out any of the other riders. After two hills, he's tied for three points with Freddy Bichot who won the second climb, and Stephane Auge is tied for second at two. At which point he has a choice: Try to stay ahead for the third climb, and probably finish 5 minutes behind the pack at the end, or fall back to the pack, have his teammates give chase to the rest of the breakaway, and try to win the final points of the day from the group, having had a chance to recuperate, and safe in the knowledge that his 3-point lead over the rest of the pack means that the only other riders with any motivation to contest the last hill are too tired from their long breakaway to do so.
Millar chose to fall back. Auge chose to stay out front -- and Auge did in fact make it to the next climb, barely, and picked up three points for a total of five. Millar was not expecting this, but he was able to take second from the pack, whereas Auge was dropped by the pack and lost several minutes at the end. When there's a tie, it's broken by overall placement, so this puts Millar in the coveted polka-dot jersey tomorrow morning, and Tuesday morning too. Quite an accomplishment for the Brit on his home turf.
And meanwhile I keep finding it amusing to read about the "Côte de Farthing Common".