There was only one trouble: the immenseness of Jupiter’s unknown wastes scared me. Fear was a new sensation for me. I got as far as Jupiter’s moon Ganymede, a thriving world bigger than Mercury, and suddenly, with great Jupiter looming overhead in the sky like a bloated overripe tomato, I knew I wasn’t ready for it. I’ve been to a lot of places and done a lot of things, and this was the first time I’d ever drawn back from an adventure.

I dallied on Ganymede for a couple of days, not knowing quite where to turn. Then one night in a bar someone hinted to me that something funny might be going on on Jupiter’s largest moon, Callisto, and I set my sights there.

It seemed Callisto had recently clamped down on tourists, had booted out a couple of newspapermen, and had done some other mighty peculiar things, and rumors were spreading wildly about what might be taking place there.

It looked like a fine idea, at the time: go to Callisto, find out what the trouble was, spend a few days putting things in order. It was the kind of jaunt I thrive on, the sort of thing that’s been my specialty since I began roaming the spaceways. By the time I was through on Callisto, I thought I’d have the blood flowing smoothly in my veins again, and I’d feel more like tackling the Big Project: Jupiter.

Only Callisto wasn’t the picnic I thought it would be. It turned out to be something more than a refresher for weary adventurers. I found that out as soon as I got there.

It had been rough to get a passport, but I finally signed on a slow tug as a mechanic, and that was good enough to get me a landing permit for Callisto.

I helped pilot a tugload of heavy crates from Ganymede to its nearby twin moon, Callisto. I didn’t know what was in the crates, I didn’t ask, and I didn’t care. The job was getting me to the place I wanted to get to, and that was what counted.