Free ARM by Larry Niven Page B

with the damn thing.”
    “Sure he was,” Porter said. “He wouldn't have been showing it around otherwise.”
    “Or calling Bertha for a backpacking expedition. Or spreading rumors about what he had. Yeah. Sure, he knew everything he could learn about that machine. Julio, you were cheated. It all depends on the machine. And the bastard did wrack up his arm, and we can prove it on him.”
    We piled into Ordaz's commandeered taxi: me and Ordaz and Valpredo and Porter. Valpredo set the thing for conventional speeds so he wouldn't have to worry about driving. We'd turned the interior chairs to face each other.
    “This is the part I won't guarantee,” I said, sketching rapidly in Valpredo's borrowed notebook. “But remember, he had a length of line with him. He must have expected to use it. Here's how he planned to get out.”
    I sketched in a box to represent Sinclair's generator, a stick figure clinging to the frame. A circle around them to represent the field. A bowknot tied to the machine, with one end trailing up through the field.
    “See it? He goes up the stairs with the field on. The camera has about one chance in eight of catching him while he's moving at that speed. He wheels the machine to the edge of the roof, ties the line to it, throws the line a good distance away, pushes the generator off the roof, and steps off with it. The line falls at thirty-two feet per second squared, normal time, plus a little more because the machine and the killer are tugging down on it. Not hard, because they're in a low-inertia field. By the time the killer reaches ground, he's moving at something more than, uh, twelve hundred feet per second over five hundred ... uh, say three feet per second internal time, and he's got to pull the machine out of the way fast, because the rope is going to hit like a bomb.”
    “It looks like it would work,” Porter said.
    “Yah. I thought for a while that he could just stand on the bottom of the field. A little fooling with the machine cured me of that. He'd smash both legs. But he could hang on to the frame; it's strong enough.”
    “But he didn't have the machine,” Valpredo pointed out.
    “That's where you got cheated. What happens when two fields intersect?”
    They looked blank.
    “It's not a trivial question. Nobody knows the answer yet. But Sinclair did. He had to; he was finished . He must have had two machines. The killer took the second machine.”
    Ordaz said, “Ahh.”
    Porter said, “Who's K?”
    We were settling on the carport. Valpredo knew where we were, but he didn't say anything. We left the taxi and headed for the elevators.
    “That's a lot easier,” I said. “He expected to use the machine as an alibi. That's silly, considering how many people knew it existed. But if he didn't know that Sinclair was ready to start showing it to people—specifically to you and Janice—who's left? Ecks only knew it was some kind interstellar drive.”
    The elevator was uncommonly large. We piled into it.
    “And,” Valpredo said, “there's the matter of the arm. I think I've got that figured, too.”
    “I gave you enough clues,” I told him.
* * * *
    Peterfi was a long time answering our buzz. He may have studied us through the door camera, wondering why a parade was marching through his hallway. Then he spoke through the grid. “Yes? What is it?”
    “Police. Open up,” Valpredo said.
    “Do you have a warrant?”
    I stepped forward and showed my ident to the camera. “I'm an ARM. I don't need a warrant. Open up. We won't keep you long.” One way or another.
    He opened the door. He looked neater now than he had this afternoon despite informal brown indoor pajamas. “Just you,” he said. He let me in, then started to close the door on the others.
    Valpredo put his hand against the door. “Hey—”
    “It's okay,” I said. Peterfi was smaller than I was, and I had a needle gun. Valpredo shrugged and let him close the door.
    My mistake. I had two-thirds of the puzzle,