>As you leave the building, Hugh and Cheren will come out to talk about you, but then a Team Plasma Grunt will run off! Oh no! Of course, before Hugh runs off to chase him, Colress exits the building and says some stuff before Hugh finally charges.
So yeah, go south to the Driftveil Dock. There will be a big boat that will contain multiple Team Plasma Grunts. You'll be versing a few grunts, so be sure to heal your Pokemon. :)
Hope I helped. :)