Tom and Abdullah, who were fussing around the engines, heard that. They knocked off what they were doing and began asking him questions--I suppose he thought they were awfully silly, but he answered all of them patiently--about horses and riding. I was looking at a couple of spare power-unit cartridges, like the one Al Devis had strained his back on, clamped to the deck out of the way. They were only as big as a one-liter jar, rounded at one end and flat at the other where the power cable was connected, but they weighed close to two hundred pounds apiece. Most of the weight was on the outside; a dazzlingly bright plating of collapsium--collapsed matter, the electron shell collapsed onto the nucleus and the atoms in actual physical contact--and absolutely nothing but nothing could get through it. Inside was about a kilogram of strontium-90; it would keep on emitting electrons for twenty-five years, normally, but there was a miniature plutonium reactor, itself shielded with collapsium, which, among other things, speeded that process up considerably. A cartridge was good for about five years; two of them kept the engines in operation. The engines themselves converted the electric current from the power cartridges into magnetic current, and lifted the ship and propelled it. Abdullah was explaining that to Murell and Murell seemed to be getting it satisfactorily. Finally, we left them; Murell wanted to see the sunset some more and went up to the conning tower where Joe and Ramón were, and I decided to take a nap while I had a chance. 8 PRACTICE, 50-MM GUN It seemed as though I had barely fallen asleep before I was wakened by the ship changing direction and losing altitude. I knew there were clouds coming in from the east, now, on the lower air currents, and I supposed that Joe was taking the _Javelin_ below them to have a look at the surface of the sea. So I ran up to the conning tower, and when I got there I found that the lower clouds were solid over us, it was growing dark, and another hunter-ship was approaching with her lights on. "Who is she?" I asked. "_Bulldog_, Nip Spazoni," Joe told me. "Nip's bringing my saloon fighter aboard, and he wants to meet Mr. Murell." I remembered that the man who had roughed up the Ravick goon in Martian Joe's had made his getaway from town in the _Bulldog_. As I watched, the other ship's boat dropped out from her stern, went end-over-end for an instant, and then straightened out and came circling around astern of us, matching our speed and ejecting a magnetic grapple. Nip Spazoni and another man climbed out with life lines fast to their belts and crawled along our upper deck, catching life lines that were thrown out to them and snapping onto them before casting loose the ones from their boat. Somebody at the lock under the conning tower hauled them in.