The bat master in the Sepulcher is Karos Razok.  If you have already met him, then I can give you a bat to fly back to him.$B$BOur bats will always fly to the Undercity, but to travel to more remote locales their rider must first visit the area and speak with its bat master.$B$BYou have met Karos in the Sepulcher, so you may now fly bats there.  Speak with me again when you are ready.