From the Game's Afterword:
Thou Spy Hath Embrangled Me is a single-scenario role-playing game for 2-3 people. The suggested player roles are that of a GM, or game master to run the adventure, and a player to fill the role of Petulla Mary Caston, a literal 'Jane Bond' of her time, which is 1567. An additional player could represent the role of her love interest, her 'Bond Boy' as it were, William Swanwick Geddes, but this is optional.
The play of Thou Spy Hath Embrangled Me is highly focused, intending to represent a classic James Bond movie in 1500's terms, using actual historical research as its foundation. For this reason, the plot flow must remain highly structured, this is without question a plot 'on rails', from which only marginal deviation can be allowed. Far from being a handicap, this is deliberate, maintaining the focus on the subject matter and theme. The value of playing Thou Spy Hath Embrangled Me is not the freeform experience of an open-ended RPG, but is instead to slip into the skin of a specific person in a specific time and place, and to live the most important adventure of her life, and nothing less, and nothing more. In short it is to play a very specific role, as fully as possible. Like the holodeck of Star-Trek, or the body-snatching of Quantum Leap, the player is expected to become Petulla (and possibly William) and see a specific circumstance to a conclusion. However, this circumstance can have any number of outcomes.
If Petulla fails, then history will be disrupted, and Lord Henry will become king of England, England will become ruthlessly Catholic, a new Inquisition will begin, and Scotland will likely dominate the British Isles politically for centuries to come. More than this, hundreds of thousands of people will perish of the Ague, and London will almost certainly become a ghost town.
If Petulla wins, then history will be as we have known it, and will utterly fail to record the very first British Superspy.
Thou Spy Hath Embrangled Me is a specific one-shot, focused role-playing scenario, but with only a small bit of imagination, and adaptation of existing spy movies to time and place, the adventures of Petulla Mary Caston could conceivably continue.
The mechanics of the game are likewise focused to the genre and to immediate and simple action with a focus on narrative. This is to be understood, and nothing more expected of them.