Emily. Age: 32.
You will be treated to a few scenes, and then you will need to track down N in the castle and confront him.
Desiree. Age: 25.
Talk to the Plasma Grunt and you can be teleported away. Create your Reshiram-catching party. You may need four to six Timer Balls. After beating the Elite Four, activate the glowing statue to descend into the mountain.