You found Latias at Southern Island. Just as things were going well, someone else caught up to you. It was Matt, and a grunt of Team Aqua is there with him.

The name's Matt! That's Team Aqua Admin Matt to you! What I want from you is that Latias behind you there. But that Mega Stone… We of Team Aqua are definitely gonna need the transcendent power of Mega Evolution to achieve our ambitions. How 'bout it? If you get out of our way, we won't rough you up.