From the White Wolf site:
The Tuatha Dé Dannan is a new pantheon for your Scion cycle. This section contains everything you’ll need, including the gods of the Tuatha, a complete 1 to 10 dot write up of their pantheon Purview, new Birthrights, new allies, new antagonists, details on their Overworld and Underworld, a new Titan that plagues the Tuatha and two sample Scions (one hero and one demigod) so you can jump right into the game.
The Scion Companion is a joint venture between our traditional and alternative publishing divisions, to provide you periodical content for Scion without leaving behind fans to love our hardcover books. The first four sections will be released as individual PDFs over the course of the next several months. The final two sections of the book (a third pantheon and a new background for Scion cycles) will appear in the final release of the Scion Companion, which will be for sale online and in stores as a hardcover book, as well as a complete PDF release combining all of the sections.