Although billed as the game's "Moderator's Guide" this book is really a wonderfully-detailed introduction to Poseidon, the Blue Planet itself. GMs running games where characters have spent a long time on Poseidon may wish to consider giving them limited access, while people in search of a detailed setting for just about any game - particularly a science-fiction, visiting other worlds one - might find it of use even if they don't particularly want to play the Blue Planet RPG.

The first page is scene-setting, a short story about a National Geographic photographer arriving on Poseidon with a mission to get a picture of an aboriginal for the magazine's front cover. In a way, this sums up what makes this game different from so many others. Fascinating as the life of a photo-journalist might be, it's not the first thing that most of us think about when creating a character from a game, yet this fits wonderfully into the Blue Planet concept.

Then comes the Foreword, which is the one bit directly addressed to the GM. This consists in the main of ideas about designing campaigns and setting the mood of your games and provides a few thought-provoking ideas even for an experienced GM.

The vast majority of the rest of the book is devoted to a detailed description of Poseidon: history, geology, ecology, geography and oceanography. It's all wonderfully detailed, and every corner is packed with little snippets that inform local colour and inspire ideas for adventures... and that's before you start reading the 'Access Denied' sidebars where specific scenario seeds are supposed to be located! The whole place comes alive with loads of detail, enabling you to be confident about running adventures just about anywhere on Poseidon.

At a quick glance, a GM might think that this book ought to be open to players as well, particularly those whose characters are not newcomers to Poseidon. But there is too much of the hidden background, material that might feature in your adventures, for this. The way it's interwoven makes for a good and inspiring read, but it does mean that you can never say, "Read the section on Second Chance" to a player who is trying to find out about that particular settlement.

After Chapter 1: The New Frontier, we come to Chapter 2: Beyond the Frontier which looks in more detail at the oceans of Poseidon. This starts off with a survey of the basics of underwater effects - pressure, light penetration, temperature, currents, etc. - to the sort of level that a diver might know. It tries to clear up popular misconceptions and provide a solid scientific footing for what follows. The next bit starts to look at the ecology of Poseidon's oceans, what you are likely to find there and how it all links together into a coherent whole. There are plenty of dangers to encounter, from storms and bacterially-infected water to actual creatures that might wish to make you their lunch. Each beastie is presented with behavioural and appearance details as well as combat stats, so characters who have ecological interests can be encouraged to study them during their explorations.

Chapter 3 is called 'Alien Legacy' and opens with the transcript of a necropsy of what is believed to be a sentient species native to Poseidon. This moves on to a detailed discussion of the native 'aborigines' who are intended to become a major plot element and source of mystery for the game. This is a chapter that players should definitely avoid! It explains what they are like - biologically and psychologically - as well as how they fit into the environment... and why they are there! Suffice to say this is something nobody on Poseidon (except, perhaps, the Aborigines themselves) know, and GMs should be wary of how quickly and how much of this they reveal during the course of their campaign. Full disclosure could alter the entire pattern of life on Poseidon. The chapter winds up with a collection of myths and legends about the aborigines, mostly wildly inaccurate, but who can say? Good ones to feed to inquisitive characters and watch them investigating all manner of false trails.

The final chapter is called 'A World of Hurt' and details the state of affairs back on Earth. There's a lot of political background: structures, personalities, organisations and history... enough to make players glad their characters have gone to Poseidon (or make them want to leave if you choose to start your game there. It's not just Earth, the whole Solar System is covered. Although it's brief, there is enough should you want to run parts of your campaign here.

Overall, this provides a lot of resources to enable the GM to make his campaign come to life: background, atmosphere, plots and plans of people already there... this is a living world your characters are visiting.