Introducing some of the places the party might visit within the Third Horizon, the first part of this book is suitable for both players and GMs. The descriptions focus on the main planet of each system covered, and on one city on that planet. The GM's part contains an overview of the history of the Third Horizon, a good look at who actually built the Portals that enable interstellar travel and provides a system for creating systems and planets of your own.
We then dive directly into the first section. Six systems are described: Algol, Mira, Dabaran, Sandaal, Zalos, and Odacon. For each, there is plenty of flavour text describing what sort of things you are likely to find on a visit - although somewhat more hard-hitting than the average tourist brochure... even the Rough Guides don't tell you where the slave market is in a place where slavery is prohibited! On a more pleasant note there are festivals, interesting sights to see and places to visit, as well as notes on the current political scene and other opportunities. Continuing the themes presented in the core rulebook, this section presents rich and strange worlds that prove fascinating in their own right, even before you consider the plots that have brought you there.
Moving on to the GM's section, we begin with an overview of history with a particular focus on the Third Horizon's troubled relationship with the First and Second Horizons... something that has been mostly forgotten by the denizens of the Third Horizon. The First Horizon is Earth (Terra), the Second Horizon is the first round of colonies and ended up dominated by a bunch of Mystics. Both Horizons viewed the Third Horizon as a good source of natural resources, a view that inevitably leads to trouble when the people living there decide that they are being exploited! The odd spelling mistake (that a good proof-read ought to have caught) doesn't detract from the sweep of history that takes us through several thousand years of strife right up to the present day in a few short pages.
Next we hear about the Portal Builders, or Predecessors as they are sometimes known. Nobody's quite sure who or what they were, just that they departed a good time ago but left a lot of interesting stuff behind. We read of some of these wonders, and of the theories and opinions that have grown up around them. All is still left quite open and vague: a neat move in that should the GM decide that the party is going to discover something about the Portal Builders, he is free to invent it for himself.
A system for creating new worlds comes next. The Third Horizon is a big place, and most of the worlds and systems in it are unknown... so here's the chance to come up with your own locations, stamp your own mark on the universe. There are thirty-six known systems, but even those - if you've flipped through the relevant portions of the core rulebook - have not been described in any detail apart from a few, so there's plenty of scope. (The records might be incorrect as well...) Gas giants, asteroid belts and those rocky planets that you might be able to actually land and walk upon are all covered here, as well as advice as to how to weave the bare bones into a coherent story, describing your new place as somewhere the party might want to visit.
The final two sections consist of ideas for creating missions based on the group concept underpinning the party and notes on travel. The 'mission generator' doesn't produce adventures for you, but it does get your mental wheels turning in appropriate directions - useful if you are struggling to come up with an idea. As the tables are based around the group concept you're using, it's quite hard to get inappropriate reults. By the time you have worked through the process (rolling on various tables) ideas ought to be beginning to spawn - you may well have come up with one before you complete the process, so don't worry, just put the dice away and get writing! Finally, the Travel suggestion is packed with ideas to make travel more interesting (the party may disagree).
Overall, this has the feel of 'Stuff we would have put in the core rules but ran out of space for', which as the core rulebook is almost 400 pages long is quite understandable. It's all useful stuff and fits well with what has already been presented, well worth adding to your game.