The Wizard is worried

When Udlotwin called on me the other day he looked so distraught and haggard that I barely recognized him. I'd never seen him like that before.

I should explain that Udlotwin (that's not the name most people know him by, of course) is a wizard. We'd been friends for years. I've often wondered why he took to me, since he told me very early on that I had no gift for magic whatsoever. Perhaps that might be why he liked me: other people might have pestered him to teach them some magic, or at least demonstrate some; by I accepted what he said and never bothered him further on the subject.
   He slumped into a chair and begged for a glass of water. When he'd drunk this, and was looking a little better, I obviously asked him what the trouble was.
   "Did you ever meet Geoffrey Dakin?" he asked me.
   "No,but I seem to remember your telling me about him. He wanted to become a magician, you said".
   "Yes, he did. And he had some of the necessary ability; just a little. That was the trouble: he'd have done better to keep well away. That's what I advised him, but he didn't listen. When I heard he'd died suddenly, with no obvious physical symptoms, I immediately suspected the worst. I managed to get into his flat,and my worst fears were confirmed".
   "Why, what did you find?"
   "Enough to show me that he'd being trying out some very risky ideas; fortunately without any success. But then I found something really important. To a layman it might have seemed no more than a simple wooden fruit-bowl; but I knew what it was: a Horn of Plenty. I wondered where on earth he could have got it".
   "What's a Horn of Plenty?"
   "A famous magical device! Things that are placed inside it multiply, and go on multiplying".
   "You mean if I put some money in, more and more money would come out?"
   "That's just what a layman would think, and probably what poor Geoffrey did think. But there's much more to it than that. A Horn of Plenty is basically a machine, and it works just like any other machine. It won't function without an input of energy; but it's a special kind of energy, which it takes from the magician. Even I would find it exhausting. You, as it happens, don't possess any of this energy. Geoffrey had some, but not nearly enough for this task. I guessed that was what killed him - though of course it might have been something different; something much more sinister. I won't go into that".
   "So what did you do?"
   "I took the Horn away. I couldn't leave it lying about: you never know who might get their hands on it. But just carrying it for any length of time would tire me out. I needed somewhere safe to hide it. So I cast around until I located a Doorway".
   "A Doorway? What's that?"
   "It's an entrance to a different world: a different universe. It'd be easiest for you to understand if you think in terms of multiple dimensions. This particular Doorway appeared to be just a hollow tree. I thought it might be safe to hide the Horn there. So I opened the Doorway".
   "And what did you find there?"
   "Initially, nothing much. A great heap of stones was completely blocking the other side. But I sensed that something, or someone, was there. And at that same moment it sensed me. A picture formed in my brain of a monstrous being, something like an enormous gorilla, but with a face like no creature of this world, ferociously shaking the bars of a cage. And its voice was yelling at me. "Let me out!" it shouted, "Let me out!" And it knew I had the power to release it, and I knew that was what must be prevented at all costs.
   "It was so overwhelming that I utterly lost control of my mind. I collapsed. I've no idea what happened next. When I recovered consciousness, I found myself lying on the grass in a strange park I'd never seem before. A well-meaning passer-by asked me if I was all right, and helped me to my feet. I was so weak I could hardly stand. And the Horn of Plenty was gone.
   "What had happened? Had I dropped it somewhere? Worst of all, had I perhaps left it beyond the Doorway, where that ..... that THING ...... could get hold of it?

"What am I going to do now?"