The Long Earth

physics post at Princeton. Now he earned his money as a peripatetic tutor at UW, and with the rest of his time – well, nobody quite knew what he did with the rest of his time. Though Jansson had found traces in the records that he’d done some work for Douglas Black, the industrialist, under another name. That was no great surprise. These days almost everybody ended up working for Black one way or another.
    Whatever Linsay was up to, he wasn’t keeping goats in his living room. Maybe it had been malicious all along, some busybody neighbour trying to make trouble for the oddball guy next door. You got that sometimes.
    But the next call had been different.
    Somebody posted online a plan for a gadget he or she called a ‘Stepper’. You could customize the design, but it would be a portable gadget with a big three-position switch on top, and with various electronic components within, and with a power lead plugged into … a potato?
    The authorities noted this, and became alarmed. It
looked
like the kind of thing a suicide bomber would strap to his chest, before taking a stroll down State Street. It also looked like the kind of thing that would appeal to every kid in the world who could knock one up from spare parts in his or her bedroom. Everybody thought the word ‘potato’ must be a cover word for something else, like a slab of Semtex.
    But by the time a car had been dispatched to the Linsay place, due to rendezvous with Homeland officers at the scene, a third call had come in, entirely separate: the house was on fire. Jansson had been part of the response to that. And Willis Linsay was nowhere to be found.
    It was arson. Forensics had found the oily rag, the cheap cigarette lighter, the heap of papers and smashed-up furniture that had started it. The purpose of the fire seemed to have been to destroy Linsay’s heaps of notes and other materials. The perp could have been Linsay, or else somebody out to get him.
    Jansson had the feeling it had been Linsay himself. She’d never met the man, never so much as seen a photograph. But her tangential contact with him had left impressions in her mind. He was clearly ferociously intelligent. You didn’t get to do physics at Princeton otherwise. But there was something missing. His home had been a disorderly jumble. The neither-one-thing-nor-the-other fire attempt fitted too.
    But what she didn’t understand was what it was all
for
. What had he been up to?
    Now Jansson found Linsay’s own Stepper, the prototype, presumably. It was in the living room, sitting on the mantelpiece above a fire that hadn’t been lit in decades. Maybe he’d purposefully left it behind to be found. The forensics guys had seen it and abandoned it, heavily dusted for prints. It would probably be taken into store once the crime scene was broken down.
    Jansson bent to inspect it. It was just a clear plastic box, a cube, about four inches on a side. Forensics thought the box might once have contained antique three-and-a-half-inch floppy discs. Linsay was evidently the kind of man who kept junk like that. Through the clear walls you could see electrical components, capacitors and resistors and relays and coils, connected with twisted and soldered copper wire. There was a big three-way switch on the lid, the positions labelled by hand with a black marker pen:
    WEST – OFF – EAST
    Right now the switch was set to OFF .
    The rest of the box’s volume was occupied by … a potato. Just a potato, no Semtex or acid vial or nails or any other element of the modern terror arsenal. One of the forensics boys had suggested it might be used as a power source, like the classic potato-run clock. Mostly people thought it was just a symptom of lunacy, or maybe some bizarre practical joke. Whatever it was, this was what kids all around the planet were racing to assemble right now.
    The Stepper had been found holding down a bit of paper on which had been scrawled, in the same marker pen, the same hand, TRY ME. Very Alice in Wonderland. Linsay’s parting shot. It occurred to Jansson that none of her colleagues had actually followed the instruction on the paper scrap: TRY ME.
    She took the box, held it; it weighed nothing. She opened the lid. Another scrap of paper, headed FINISH ME, had simple instructions, what looked like a draft of the circuit diagram that had finished up on the net. You were supposed to use no iron parts, she read; that was underlined. She had to finish winding a couple of coils of