The book is much smaller than the others in the series, clocking in at "only" 148 pages! The ENTIRE book is made up of army lists - much in the same style as the army list sections in the Core rulebook and in The Deluge rebook. You get a few paragraphs describing the army background, then a listing of any new special rules (but existing rules are not duplicated here!), and then straight into the army list. Many of the lists in here are from the BFAS downloads section and have existed previously as PDFs. Whether or not they will continue to be available as downloads, I have no idea, but for now, they're all still there.
First up we have the new Skirmish lists...19 of them to be exact! The very first list shows off a new concept that is repeated several times throughout the book - dual nationality lists, first shown in the Polish-Transylvanian Skirmish Force of November 1653. Oddly, specific, eh? The list contains the standard Polish Cossack Style Cavalry, Polish Tartars, and Wallachians, and also contains Transylvanian Szekely cavalry and Mounted Handgunners. As far as army-wide special rules, the force retains the Polish ones (and not the Transylvanian ones). For league/campaign/tournament purposes, the list counts as Polish unless you have over half of your units as the Transylvanian options, then it becomes Transylvanian. While the list has two commanders (one Polish, and one Transylvanian), it will provide some unique command and control challenges as the Transylvanian commander cannot do anything to the Polish units!
Next, we have some Divisional lists. Many of these are specific historical divisions, based with a named commander and special rules to reflect a specific Division at a specific battle/time period. Sobieski's division is reprinted here, with some flight changes....did someone say 14 FSP Winged Hussar regiment? There are some dual-nationality skirmish lists, but they are also still specific historical lists, since the core divisional rules allow allies already. There are a couple of 3-way alliance lists, such as a Swedish Allied Vanguard list that also contains Imperials, Cossacks, and Transylvanians.