Make sure you go through the southern exit of Route 13 to get to Lumiose City. Flying there or walking to the Route 4/5 exits, as that will leave the power out.
Have you seen a really tall guy who is in search for the mysterious flower Pokemon?
Did you see two people in masquerade masks that give you some Full Restores and something else?
Make sure you do/see/get all those things. If you have done all of them, I've got nothing. xD
Hope I helped. :)
Source and Experience