Each PACG product series is inspired by an AP (Adventure Path) from the TTRPG line. An AP consists of 6 connected, sequential Adventures. In PACG, someone needs to have purchased the matching Base Set to play any part of an AP - although cards are compatible, there's currently no official way to blend scenarios from different APs. (This will likely change in the upcoming 5th product series! It's said to be universal. -ed).
Each Adventure in the original AP is converted to an Adventure Deck - 110 cards including five scenarios and many new boons and banes. It's technically not required to play these adventures in order, but that's the recommended approach for most players. The first Adventure Deck comes in each Base Set- but even before you open this box within a box, the Base Set already includes a B-level adventure that sets up the AP's story.
There is one additional PACG product in each AP product line: a Character Add-On Deck. These add new playable characters, some new boons/banes, and overall add enough cards that 5-6 players can play at once (Base Sets only support 1-4 players by themselves).
Released AP Product Series
Announced Adventure Paths
Curse of the Crimson Throne