o," he
said finally. "What mistake did I make?"

"None that I know of," Barney said. "But you're doing everything you
can to keep the world from learning about the McAllen Tube. At the
same time you've kept it in operation--which made it just a question
of time before somebody else noticed something was going on, as I did.
Your plans for the thing appear to have gone wrong."

McAllen was nodding glumly. "They have," he said. "They have, Mr.
Chard. Not irreparably wrong, but still--" He paused. "The first time
I activated the apparatus," he said, "I directed it only at two
points. Both of them within structures which were and are my property.
It was fortunate I did so."

"That was this cabin and the place on Mallorca?"

"Yes. The main operational sections of the Tube are concealed about my
California home. But certain controls have to be installed at any exit
point to make it possible to return. It wouldn't be easy to keep those
hidden in any public place.

"It wasn't until I compared the actual performance of the Tube with my
theoretical calculations that I discovered there was an unforeseen
factor involved. To make it short, I could not--to use your
phrasing--shut the Tube off again. But that would certainly involve
some extremely disastrous phenomena at three different points of our
globe."

"Explosions?" Barney asked.

"Weee-ll," McAllen said judiciously, "implosions might come a little
closer to describing the effect. The exact term isn't contained in our
vocabulary, and I'd prefer it _not_ to show up there, at least in my
lifetime. But you see my dilemma, don't you? If I asked for help, I
revealed the existence of the Tube. Once its existence was known, the
research that produced it could be duplicated. As you concluded, it
isn't really too difficult a device to construct. And even with the
present problem solved, the McAllen Tube is just a little too
dangerous a thing to be at large in our world today."

"You feel the problem can be solved?"

"Oh, yes." McAllen took off his glasses and rubbed his eyes. "That
part of it's only a matter of time. At first I thought I'd have
everything worked out within three or four years. Unfortunately I
badly underestimated the expense of some of the required
experimentation. That's what's delayed everything."

"I see. I had been wondering," Barney admitted, "why a man with
something like this on his mind would be putting in _quite_ so much
time fishing."

McAllen g