InterWorld by Neil Gaiman

‘mudluffs.’ That’s an acronym, MDLF, standing for multidimensional life-form. Which is kind of a pointless label, I know—we’re all multidimensional life-forms, right? Except that you and I can only move freely in three dimensions and linearly in a fourth, whereas they have complete freedom in who knows how many. Including, in many cases, the fourth.”
    Now, most of what he was saying was going so far over my head that I feared for local air traffic. But I’d seen Twilight Zone reruns, and I knew what the fourth dimension was. “You mean they can travel in time?”
    “We think some can. It’s hard to tell, because there’s a certain temporal flexibility between the planes that can affect all of us. You learn to compensate for it when you Walk—otherwise you can spend a month on one world and find that only a couple of days have gone by in another one. It gets real confusing real fast, so we try to take advantage of it only when absolutely necessary.
    “But that’s not important now. My point was the mudluffs—stay away from them. They aren’t intelligent, but they can be dangerous. Usually they stay in the In-Between, but some of ’em know how to squeeze out, like polydimensional toothpaste, into the various worlds.”
    I was feeling pretty overwhelmed by all this, and starting to wonder how much of what Jay was telling me was real and how much was just him yanking my chain. “Right. Next you’ll be telling me they’re the ones responsible for all the legends of fairies, goblins, like that,” I said. I expected Jay to laugh, but he shook his head.
    “No, those are usually HEX scouts. Binary scouts tend to be seen as ‘gray men’ and all that other Roswell crap. But I think some of the tales of demons probably began with mudluffs. But you’ll get all that in your basic Altiverse studies. All that matters now is making sure we don’t run into any of ’em, and getting out of the way if you do.” He grabbed me, turned me and gave me a push. “What’re you waiting for? Shock’s pretty much worn off for me, and this hexburn is starting to hurt . I want a hot bath and a bloodstream full of painkillers. So pick ’em up and put ’em down, Walker! You know the way! Hit it!”
    I started to tell him again that he had the wrong guy—but then I stopped. I looked ahead of us, into that crazy swirling Mandelbrot brew called the In-Between, and somehow I realized he was right.
    I did know the way.
    I don’t know how I knew—I don’t even know how I knew that I knew. But the route was there, clear and shining in my head. It wasn’t self-deception this time either. This was the real thing.
    Simultaneously with that realization, I knew something else—that Jay was right about the mudluffs. There were critters out there that would make two bites each of us and use our leg bones for toothpicks. I didn’t want to run into any of them, and the longer we stayed in the In-Between, the greater the risk of doing that became. They could track us down with senses we don’t even have names for.
    I started moving, and Jay followed. He hopped onto my purple pathway and we stuck to it for a while, ducking under writhing Möbius strips and pulsating Klein bottles. Gravity—or whatever the force that kept us on the path was—seemed to be off and on. When I realized that the time had come to leave the purple ramp, the only way to do so was to jump off. That took some guts, if I do say so—it looked like I was jumping into an abyss that made the dive off the ship seem puny by comparison. But the way was shining bright and clear in my head, so I held my breath and stepped off.
    My stomach tried to claw its way up my throat and escape, the entire In-Between rotated ninety degrees in several directions at once—and then “down” wasn’t down anymore. I floated among the lazily drifting geometric forms, past what looked like a partly open wardrobe that gave a glimpse of an inner door leading to a wondrous,