Free Night Mare by Piers Anthony

and a balloon of steam and smoke went up.
    “Ha ha, mare, he’s putting it out!” the nix called from a safe distance across the moat Apparently he felt that it was best to join sides with the monster. “I guess that knots your tail!”
    “You shut up!” Imbri projected in a dream that encompassed both nix and centycore. “He won’t get it all!”
    “That’s what you think, horsehead!” the nix cried.
    Encouraged by this, the monster indulged in a fever of mudslinging. His aim was good; more gouts of smog ballooned out. The fire was furious, but was taking a beating.
    “Curses, he’s doing it!” Imbri projected with wonderfully poor grace.
    Indeed he was. Soon the fire was largely out and smoke suffused the entire region, making them all cough. The light of the sun diminished, for sunrays didn’t like smelly smog any better than anyone else did.
    Was it dark enough? Imbri wasn’t sure. “If this doesn’t work, we’re finished,” she projected privately to Chameleon. “Maybe you should dismount.”
    “I’ll stay with you,” the woman said loyally. Imbri chalked up one more point for her character, though she realized it might be fear of the monster that motivated Chameleon as much as support for Imbri.
    Now the centycore reoriented on them. “You’re next, mareface!” he cried, and charged.
    Imbri bolted for the megalith nearest the fire, where the smoke hovered most thickly. The centycore bounded after her. He was sure he had her now.
    The mare leaped right into the stone column—and phased through it. Chameleon, in contact with her, did the same. The darkness was deep enough!
    The monster, following too closely, smacked headfirst into the column. The collision jammed several points of his antler into the stone, trapping him there. He roared and yanked, but the stone was tougher than the ice had been, and he could not get free. That particular menace had been nullified.
    Actually, Imbri now recognized an additional concern she hadn’t quite thought of before. She had not been certain she could phase a rider with her. She had brought the ogre out of the gourd, but he had already been in it, his body separate. She had carried the girl Tandy once, but that had been in genuine night. When she phased out of the Horseman’s pen, she had left the hobble behind, and it had certainly been in contact with her body. So the precedents were mixed. Apparently she could take someone or something with her if she wanted to, and leave it behind if she chose. It was good to get such details straight; an error could be a lot of trouble.
    Now they could explore the center of the stone structure. They moved in cautiously.
    There was a rumble, as of a column wobbling in its socket and beginning to crumble. Some sand sifted down from one of the elevated slabs. Both mare and woman looked up nervously. What was happening?
    The noises subsided as they stood. Apparently it was a random event, possibly the result of the heat or smoke of the recent fire.
    Imbri took another step forward. There was a long, moaning groan to the right, causing their heads to snap about. It was just another massive stone column settling, doing nothing.
    Again Imbri stepped forward. The huge rock slab above slipped its support and crunched down toward them.
    Imbri leaped backward, whipping her head around and back to catch Chameleon as the woman tried to fall off. The massive stone swung down where the two of them had been the moment before, thudding into the ground with an awesome impact.
    “This place is collapsing!” Chameleon cried. “Let’s get out of here!”
    But Imbri’s memory was jogged by something. “Isn’t it strange that it should collapse the very moment we enter it, after standing for what seems by the cobwebs and moss to have been centuries?” Actually, cobwebs could form faster than that, but Imbri wasn’t concerned about minor details. “This resembles the handiwork of the spriggan,” she concluded in the