From publisher blurb: The first Thunderscape adventure path begins here! Times are tough for adventurers in Aden, and the high-paying bounties offered by the Cogswheel Irregulars in Mekanus are a great place to save up a few crests for traveling. As representatives of the Urbanan government, however, the player characters soon find themselves in the crosshairs of a group eager to retrieve forgotten secrets from the most dangerous parts of the city, and they are only the first ones to paint a target on the characters' backs! Heart of the Machine includes the following: An adventure in four acts! A primer and map of Mekanus, the largest city in the Known Lands! Details on the mercenary lawmen known as the Cogswheel Irregulars! New NPC profiles and bestiary entries! And much more!