After passing through Route 5 Versant Road which is west of Lumiose City, you reach Camphrier Town.
Meet Cassius
Go into the house near the Route 5 exit of Camphrier Town to meet Cassius, who is running the Kalos PC Box. Talk to one of the girls in this house to receive TM46 Thief.
Visit the Pokémon Center
The Pokémon Center of Camphrier Town is south of Cassius's house. Inside of this Pokémon Center is the Name Rater. He can change the nicknames of your Pokémon, but he can't change the names of pokémon that were traded to you after being raised by a different trainer.
Explore Town
The guy walking around in front of the Pokémon Center will give you an Ultra Ball.
To the west of the Pokémon Center is Hotel Camphrier. Talk to a guy in the lobby to get a Full Heal.
Go upstairs in the hotel. In the far right room, you find Mr. Bonding, who gives you Sp. Atk Power.
Outside, go southeast from the hotel to find a narrow passage in the grassy area. Go to the end of the path to find a Star Piece.
There is a fountain just north of the hotel. Go west from the fountain and talk to the person there to get Berry Juice. Go into the house above this person and talk to the woman at the sink to get a Sweet Heart. A guy in this house will ask to see a specific type of pokémon and will give you an item if you show him one.
Go outside and go southwest from the house with the guy who asks to see a specific type of pokémon. There is a ledge south of the western exit of town. Jump down that ledge to find an X Attack.
Visit Shabboneau Castle
In the north middle of town, you find a drawbridge leading to Shabboneau Castle. Go inside. Shauna is there with a black belt who tells the story of Shabboneau Castle. The family who owned it gave a lot of their belongings to people, and that's why it's so empty. But he doesn't know anything about Mega Evolution.
Someone comes in and says "it's happening", so the black belt leaves to go to Route 7 because "it's that time of year again". He says that you are free to explore the castle.
Shauna wants to go to Route 7, but before you do, you should go upstairs. When you are on the second floor, go to the south end of the room. There is an Escape Rope south of the table. At the north end, there is a door to a bedroom, but there is nothing of interest there right now.
Now you should go to Route 7. Get there by using the west exit of town. Route 7 is called Rivière Walk.