A stable master is an NPC that offers hunters the opportunity to store 50 pets and retrieve them at any other allied stable master. They are typically found outside most city and town inns or near the pet trainers. You can ask the city guards where they are when you are in major cities. In other locations where city guards are not present the minimap tracking feature will show a horseshoe icon (File:MiniIcon StableMaster.png) at their locations.