The story opens up when two men, while doing repair work on a ship in orbit around Jupiter, find a bottle floating around in space. The bottle contained a note written by a man just before his ship was going to crash on Uranus, and said that he saw huge, wealthy cities on the planet below him.

The note was then forwarded to the wife of the man who wrote the note, who then gave it to her two children. The criminal who found the note, however, lured the children to a smuggler's spaceship with the intent of stealing the note. While he was gone looking for a smugglers, though, the children accidentally launched the ship -- which had a course laid in for Uranus.

The 3 Space Explorers, along with the owners of the "stolen" ship, raced after the children to Uranus. Upon landing on Uranus and finding the children the Space Explorers find that the note was right -- under large sheets of "ice" were huge, glistening cities.

The owners of the smuggler's ship were then to return to Earth -- but instead of doing so they faked the trip and landed on Uranus again. While the smugglers were in space, the Uranians met with the Space Explorers and invited them down to their city. The Uranians then brought them down to their only remaining city via an airlock in a mountain. They didn't dare drill a hole and bring them down that way -- for, as they explained, their city was covered by a living sheet of organisms that, if heated, would die and cause the destruction of their entire city.

While the Space Explorers were visiting the inhabitants of the city, the smugglers landed on Uranus again and quickly burnt a hole through the "ice". Once through, they started looting like mad. Even when it became apparent that the city was freezing the smugglers still would not leave behind their loot -- and thus they were killed, along with the rest of the fantastic city, when the organisms they had killed finally died.

This sad story, unlike the others that I have covered, has no scientific gadgets to review. It does have some interesting points, and scientific inaccuracies, though. I'll deal with the mistakes before I get on to the actual story itself.

For the first mistakes, let's look at the cover of the book. Let's ignore, for the moment, the fact that that particular scene never occurred in the book. The first thing that hit me was the fact that the Space Explorer's hands are out in the open -- despite the fact that the surface temperature of Uranus was hundreds of degrees below zero. Their hands would almost instantly freeze if left out in that kind of weather! And yet there they are -- on Uranus without even gloves. Something is definitely wrong.

The cover also has distance problems. The city is located many miles below the city of ice -- one character in the book said that he felt like he was flying high over a vast city on Earth. The cover, on the other hand, makes it look like only a few hundred feet separate the Explorers from the city. There is also the problem of the spaceship. According to the book, it was quite a hike from the spaceship to the portion of ice that held the giant city -- and yet the cover makes it look like it was only a couple hundred feet. The mountains, too, were many miles away -- but there they are, right there in the background. There is also the problem of the missing beach. The city was located in the middle of a huge field of "seaweed" -- not right up next to the lake edge. The cover, however, does not reflect this fact.

There is also the problem of the mysterious sinking ice (see page 169, about the middle of the page). On Uranus, claimed the book, gravity was about 3 times that of Earth. Therefore, if you took a glass of water to Uranus and plunked a few ice cubes in the water the ice would sink to the bottom of the glass (after all, Uranus has more gravity than Earth and therefore can pull more on the ice). Now consider this for a moment. A cubic inch of ice has less mass than a cubic inch of water. Mass determines weight. Since ice, then, has less "weight" than water, ice will float in water. It doesnít matter how much you increase gravity -- ice will always float in water! Ice has less mass than water; therefore, it floats. This is not hefty stuff, and it blows my mind that any science fiction writer could have got it wrong.

This means that the city would have frozen from the top of the lake down, instead of freezing from the bottom up (as it did in the book). This also means that had it existed in the real world it might have survived -- had they been deep enough and/or been able to heat the water, the water would not have frozen and their city would not have died.

The aliens of Uranus were a very interesting group. One of their biggest scientific achievements, in my opinion, was their ability to extract precious metals from seawater in what looked like worthwhile quantities. The ability to do this is much sought after, because the ocean contains what may be the biggest deposits of precious metals on the planet. The problem, however, is that the metals are so hard to extract -- the extraction rates are very low, the existing processes are very slow, and it takes many thousands of gallons to extract anything. I'm not sure what the problems are in the extraction, but I would imagine that there are some pretty stiff chemistry problems. Still, someday we will find a way to extract gold from the sea, and when we do we will reap enormous benefits.

One thing that I wonder at, though, is that extracting metals from the sea isn't talked about very much anymore. Years ago it seemed to be a big topic -- the Germans tried it in WWII, the Government experimented with it, and it seemed like it wouldn't be long until we had it. There was even a Rick Brant book (Sea Gold) written on the topic. Over the years, however, such a technique seems to have faded into the background. Maybe gold has become cheaper. Maybe other sources were found. I donít know -- but I would like to. What's the holdup here?

Besides the scientific mistakes the book does have some interesting points. First, the ship that the children "hijacked" was extremely interesting. Did you notice that it had enough fuel to go clear to Uranus and return? For one of today's spaceships to make the same trip it would have taken enormous quantities of expensive fuel. In fact, I'm not sure it could be done. The cost, at any rate, would have been astronomical. In the book, though, the fuel the journey ate up wasn't even brought up -- evidently fuel was not an issue here. Somehow, then, they managed to lick the need for fuel -- but how they did this with their atomic engines I'll never know.

Another interesting point is the fact that the ships were navigated completely by computers. All you had to do was put in your destination, press a button, and off you went. Once you got to where you were going you simply loaded in another reel, pressed a button, and you landed. With space travel that easy you wonder why more of space hadn't been explored. After all, if you don't have to worry about the cost, and the controls are on automatic, why not take a few voyages to the outer planets? You never know what you might findÖ

Is it really possible to make space travel that easy? I would think that, with (maybe great) difficulty, you might be able to create a computerized spaceship that could basically fly itself. That would be the easy part -- it's the fuel that's the big problem. How in the world can you eliminate the fuel problem? Where can you find a nearly unlimited and free source of energy? Even if you found this supply, how could you harness it and turn it into thrust? You see, just having enormous amounts of electricity will get you nowhere. That electricity, somehow, must be turned into thrust, and that is the key problem. Rockets are what we currently use to create thrust, but they carry a big price tag in fuel. If we could do what Tom Swift did -- that is, take normal sunlight, turn that into electrical energy, and use that to power an electrical repulsion beam and thus generate thrust from sunlight -- the galaxy would be ours.

If an answer is ever found to this key problem, the space age will really have begun. Free travel to anywhere in the solar system -- or perhaps the galaxy -- will finally be possible.

2 stars out of 5. This book is, in my opinion, the worst one of the series. Like all the Dig Allen books it wins very high marks for originality, but unfortunately this one falls down in other areas. I find it difficult to believe that the twins could accidentally launch a rocket ship to Uranus -- and both the pirates and the Uranians are too insane to be readily believable. The previous books in the series held together well with a good plot and a sense of plausible excitement that kept the reader on edge; this book lacks both. I will give the book two stars for its excellent imagination, but no more than that.