Instead of its usual mission of exploration, the Enterprise is currently tasked with transporting Dr. James Atheling to the Starfleet Academy. On the way there, they encounter a most unusual rogue planet: it is orbited by a tiny sun, and its features appear to have been deliberately constructed. They decide to investigate, but the transporters don't work, and when they take a shuttlecraft to the surface, its engines cease to function upon landing, leaving them trapped.

The planet is populated by a variety of deadly plants and animals, as well as a species, who decide to call themselves 'Arivne', after a Vulcan word, that are highly advanced and telepathic. Worse still, they are informed that another telepathic species, the Irapina, is approaching, intent on bloody conquest, though they are presently a thousand years away. Kirk, Spock, and McCoy engage in a mental battle to convince the invaders that the Federation is too strong to attempt to conquer. They succeed, and the invaders adjust course to aim for the Romulan Empire, instead.

Notes

The story lacks originality. A generically dangerous planet with some deadly beasts can be seen in any of a hundred stories. The description of Hixon, who is transformed into a 'half-Arivne', losing his eyes is reminiscent of Wells's "The Country of the Blind". The idea of a super-advanced telepathic race using what amounts to a child as an interpreter is definitely not new–we saw it one year earlier in Star Trek Log Eight.

The characterization doesn't feel too far off, though Scotty's accent is way overdone:

It makes sense that Haldeman's characters fit (though not that Scotty's accent is so off), since he had done the research:

They make some confusing choices, though. For example, they have set the shuttle down in very tall grass, and decide to set the whole grassland on fire so no creatures can sneak up on them by hiding in the grass. This seems like a bad enough idea, already, but when they actually do it:

So they set the world around them on fire without thinking that it might get hot. The temperature gets "to within one degree of the boiling point of water"–inside the shuttle, surely, since the fire must be hotter–and they survive it with nothing worse than severe thirst. Now, it is perfectly possible to survive 100°C heat, or even rather more–briefly. But by the time the temperature could have reached so high inside the shielded shuttle, they'd all have long since died, their lungs burned by the scorching air. Even if they somehow held their breaths the whole time, they'd die of heat stroke. Telepathy and teleportation and miniature black holes and all that, I can accept, but that's just a bridge too far.

Actually, this scene with the fire is something that would work much better on TV than on the page: you could see the flames licking at the windshield, the actors putting their all into displaying their discomfort, and it'd distract you from the fact that it was a rather foolish idea and they brought this on themselves.

Ultimately, though, missteps like these could be forgiven. The book's real sin is that it is boring. The landing party has set down on a dangerous planet, so they hunker down and wait for rescue. Some alien invaders need a demonstration of willpower to be dissuaded, so a demonstration is provided. There's no greater meaning to anything that happens, and no interesting questions are asked or answered. Where The Price of the Phoenix, published the previous month, was very poorly written with pretensions of larger themes, Planet of Judgment is pretty well written but doesn't even pretend to have anything worthwhile to say. It's a disappointment. Haldeman is a good, award-winning scifi author, but he cannot have been giving his best effort with this one.