You looked for Hugh in Route 20, but he wasn't there. When you continue north, you find yourself in Floccesy Ranch.
Go north to the fenced-in area to find Hugh. He will challenge you to a pokémon battle. His pokémon is level 8.
After you win, you will give Hugh the Town Map.
Look for Herdier
The husband and wife who own Floccesy Ranch will come by and give you each a potion.
Then they will say that one of their two Herdiers is missing and will ask if you have seen it. Hugh gets really upset and goes to look for Herdier.
Talk to the woman to have her heal up your pokémon. Now you need to go look for Herdier.
In the southwest corner of the ranch, you will find Lass Molly, who battles you. She has a level 6 Purrloin and a level 6 Sewaddle.
Just south of where Hugh is looking, there is a pokéball in the grass. It contains... nothing! It's a free pokéball! You can reach it from the left side.
Go north from the fenced area where Hugh is standing. He will go north past you to look for Herdier some more.
Up north, Janitor Orville will battle you. He has a level 6 Lillipup and a level 6 Mareep.
When you go east from Janitor Orville, Hugh rushes over and gives you a Parlyz Heal.
If you go east from Janitor Orville, you encounter Youngster Kenny. He has a level 6 Patrat and a level 6 Psyduck.
South from Kenny, there is a pokéball that contains an X Attack.
When you go farther east, you hear Herdier bark. Hugh runs up and says to search this area.
If you go south of where Hugh is now standing, you find a Potion. And you can see Herdier from here, along with some guy who looks like he's up to no good.
Go south and around to where the Herdier is. The guy introduces himself as a member of Team Plasma and asks if you have heard of it. Answer however you want. The guy throws TM21 Frustration at you and runs away.
Hugh and the guy who owns the ranch will come over. Hugh gets all angry again, and the owner wonders if Hugh is afraid of losing pokémon. Then the owner and the Herdier return to the ranch.
Walk west and jump down the ledges to return to the ranch quickly. If you talk to the owners, they will ask if you trained with Alder. You should go do that now! Return to Floccessy Town.