City at the Edge of Midnight

Back in the real world, a boy named Jimmy is pulled under his bed and vanishes.  In the world of Dungeons and Dragons, the kids are lost.  The Dungeon Master tells them they have to find the City at the Edge of Midnight, where children from this world and the theirs are being held prisoner.  They then find an oasis, that's inhabited by a clan of monsters.  When the monsters have them surrounded, a traveller by the name of Ramuud comes and saves them.  He then leads them away from the cursed oasis to his own encampment.  Ramuud then explains that long ago his daughter, Aisha, was kidnapped by the Nightwalker and is being held prisoner at the City at the Edge of Midnight.  Wanting to return the favor of saving them from the monsters, the kids offer their help, but Ramuud tells them that it's not nessary.  But when Bobby is kidnapped that night, they're forced to enter the City at the Edge of Midnight to fight the dreaded Nightwalker.