The Hidden Isle is set in 1572. The PCs are Agents for the Isle of Dioscoria (I keep reading this as "Discordia", but that would be a very different game), one of seven freedom loving, hyper-tolerant, states scattered around Europe and the Middle East. Missions tend toward social justice actions and political intrigue on the world stage. The intro put it best: "This is a game about swashbuckling adventures across Europe and the Middle East, stealing forbidden texts from oppressive regimes, protecting an island of outcasts using ancient magic, and toppling an empire with just the right speech at the right time."
Mechanically, the Hidden Isle is FitD without any dice - Tarot cards are used, instead. The Major Arcana + Court (face) cards (the Vision deck) are used for divination and visions - at the start of a session three or more cards are used to create the scenario. At any time, the Seer (read: GM) or any player can trigger a vision. Visions loosely map to Flashback in BitD, except the can be past, present of future and don't have to be something the agent could directly witness.
The remaining number and ace cars form the Pip deck. At the start of each scenario, each player is dealt a Fortune deck that acts more or less like FitD Stress. Skills (FitD Actions) are split into four Attributes, instead of three like most FitD games. Each Attribute maps to a a Tarot suit. When doing a Challenge, the player receives a number of cards equal to one plus the number of pips their PC has in the Skill that they are using. The Suit for the Skill's Attribute is trump for this Challenge. A PC can also leverage their ideals, burdens, vices or virtues to modify their hand before looking at it. The Seer also draws a hand based on the difficulty of the Challenge. Both the player and the Seer choose one card and reveal them simultaneously. At this point, the player can Push and allies can Assist by discarding a Fortune card to either change the suit of the played card or increase its value. If the player played trump and the Seer did not, it's an unconditional success, otherwise it's a success-with-complications or failure based on the highest number (aces high).
There are four Harm tracks, one for each Attribute. Burdens, when activated, give you an extra Challenge card, but brings it closer to being a Vice, which causes Spiritual Harm during downtime. Ideals, when activated, give you one less card, but increase the value of your cards, and brings it closer to being a Virtue. A Virtue is an Ideal without the mechanical disadvantage, but your PC needs to live up to it in the narrative to keep it.
This being such an idealistic game, killing and murder is frowned upon. There is an optional Downtime mechanic called Answering Violence which adds narrative and mechanical weight. Solo mode justifies the PC's extra stats by being setting the missions to be more Black Ops - more dangerous than the norm or skirting Dioscoria's values.
Magic does exist in the world - this being the time of John Dee and many mystic traditions. However, it is rare, and superstitions abound. Dioscorian magic is very advanced, but drawing attention to it can have repercussions and the text has many good examples of consequences, both personal and geopolitical.
The book is rounded out with the diegetic memoirs of a visitor to Dioscoria; forty pages detailing five major cities at the time (London, Lisbon, Venice, Konstantiniyye and Qazvin) to place missions in; an almost why-did-they-bother bestiary; and a short section on interpreting Tarot cards, focused on usage in the game.
Final thoughts: The game is an effective conversion of FitD to cards. A single card pick does seem overly simplistic, at first, but it's analogous to FitD's conventional single-highest-roll. Plus, it give the GM the ability to give a bit more nuance to an encounter. I like my RPGs quite a bit darker, but it's a nice change from the usual "woke" fight against capitalism, Eat the Reich, rebel against corruption. This should appeal to anybody who wants a more idealistic, less dark, default narrative. I don't have an in-person group and I think the shared decks would make The Hidden Isle a pain to run online. I haven't come across a VTT card deck implementation I've been happy with, so I don't think this will come out often. But I could see running this solo.