Now that you’ve done all the -other- things on the surface level of Castelia, it’s time to head towards that Gym.  When you arrive, though, Clyde is guarding the entrance.  He tells you that the Gym Leader, Burgh, ran off for some reason- something about some trouble going on.  This prompts a little girl with giant hair to pop up, asking about the Gym Leader.  Clyde greets her as Iris, and tells her that Burgh left.

Iris mutters something about Burgh getting ‘artist’s block’ and wandering out of the Gym on a regular basis, then greets you.  When the friendly little girl talks to you you apparently brought up something about Team Plasma, but she claims the group disbanded two years ago.  Still, she offers to help out anyways, and thinks a moment before coming up with an idea where such people might hide.  She runs off, prompting Clyde to complain to you about the similarities between her and Burgh, then directs you to follow her around to where the Pokemon Center is.

You catch up with her just as you get there, and she calls out to you to hurry up.  Iris points out that only Thumb Pier and Narrow Street stand out as suspicious places in Castelia, then heads off for the rightmost pier in the city.  Make sure your team is all healed up in the Pokemon Center, then pursue her to the pier.  You’ll catch up to her at the end of Oceanfront Road, where she runs out onto the pier.

When you get there, Iris explains that you can enter the sewers from Thumb Pier, which is ‘pretty suspicious, right?’  This is when Hugh shows up out of nowhere, asking if you’ve found Team Plasma.  Answer however you like, he’ll still know that you didn’t and head into the sewers at a breakneck pace.  Iris continues as if completely uninterrupted, leaving you to head into the sewers after your friend.  Hugh waits down the initial stairs, ready to accompany you in.  He tells you that you’ll need to get tougher, but for now he’ll handle healing your pokemon in addition to his own.  Let him know when you’re ready to go, and he’ll join you to delve into the grotty sewers together.  This means that you’ll encounter wild pokemon in twos, but you’ll still only fight opposing trainers one on one.