After passing through Shalour City and meeting your friends there, you head north to the Tower of Mastery to learn about Mega Evolutions.
When you enter the tower, you see a statue of what looks like a Lucario, but somehow different.
Go into the door at the base of the statue. You'll meet the Mega Evolution guru, and your friends will show up. The guru will ask if you were the one who found the Intriguing Stone. Answer however you wish.
Korrina is the guru's granddaughter. The guru and Korrina explain that Mega Evolution is temporary, and that not all pokémon have a Mega Evolution form. He says that for a pokémon to Mega Evolve, it needs to hold a Mega Stone, and the trainer needs to wear a Mega Ring that has a mysterious stone set into it.
But the guru only has one ring, so he asks the five of you to decide who gets it. Tierno, Shauna, and Trevor don't feel up to the challenge of using Mega Evolution, so your neighbor challenges you to a battle for the ring.
Battle Your Neighbor
Talk to your neighbor when you're ready to battle. He has a level 28 Meowstic, a level 30 starter that is strong against yours, and a level 28 Absol.
After the battle, Korrina tells you to challenge her at the Shalour City Gym.