Now I don't play card games at all, but apparently there was a collectable card game (CCG) based on the same world as the 7th Sea RPG, and this book is a 'cross-over' intended to facilitate sharing of ideas between the RPG and the CCG. The Introduction explains that much of it was intended to enable CCG players to make use of role-playing material, but that role-players may also find ideas and information to use on the table-top.
The first chapter, History, presents the storyline as used in the CCG. This involves a long and dangerous search for a mysterious island called Cabora that had long lain hidden beneath the sea, by the machinations of the mysterious Syrenth. Just about every nation and faction you can imagine got involved in this search. Plenty of swashbuckling and skirmishes, particularly at sea, ensued as all these rivals searched for a series of 'switches' that would eventually cause Cabora to arise. It all makes for an exciting and epic story and - if your party are not avid card players - could quite easily be turned into an excellent role-playing campaign. (I must confess I'm quite baffled as to how you tell such a story with a card game, though! I think it served more as background to combats between CCG players.) If you are planning such a thing, the timeline in the back of the book will be invaluable.
Then the next chapter, Factions and Places, is about turning features from the CCG into resources for your game, with detailed descriptions of the various factions used in the CCG. Each faction - and there are quite a few! - has its history, structure, tactics and notes on their crews laid out. We also hear about legendary ships and notable locations that have featured in the CCG. Plenty of scope to gather background flavour for your role-playing game here.
Chapter 3: GM's Section looks at adventures at sea and at faction-based adventures. These only work if everyone at the table belongs to the same faction, of course... unless you want a real brawl on your hands. There's also a list of all the artefacts that have turned up in the CCG complete with descriptions of their powers and abilities, a discussion of their current whereabouts, and adventure hooks that are mostly quests to retrieve the item in question. There is also all you might need to bring the horrifying legend of the Black Freighter to your table, as well as plenty of the secrets of the lost isle of Cabora itself. This includes some devilish traps which might come in handy.
Finally, Chapter 4: Rules enables you to convert personalities from the CCG into characters for the role-playing game, and to create cards for your favourite player-characters if you'd like to do that. There are some new bits and pieces for role-playing characters based on stuff in the CCG, and a swordsman school - it's the Rogers one from the Pirate Nations sourcebook - that's appropriate for characters originating from the CCG. New backgrounds, skills and items follow, along with some advanced sailing rules and ones for nautical battles. The book rounds off with two appendices, the first covering locations and a timeline for the CCG (invaluable if you want to reuse that storyline in your role-playing campaign), and the second containing full stat blocks and background information for many of the CCG's most prominent figures.
So, is this useful? It certainly is if you think that the plotline of the CCG would make a good role-playing campaign - and if your tastes lean towards derring-do on the high seas with a strong flavour of the Pirates of the Caribbean movies, it probably will - provided your players are not CCG fanatics who already know it, of course. It's certainly good to see all the hard work and imagination that went into the CCG presented in a useful form for role-players.