The Gold Ring is a cherished Cahill family heirloom. It was given to Gideon Cahill from his father. It was then given to Madeleine Cahill from Olivia Cahill to protect it. Grace was the last Madrigal to protect it before Amy. Its importance was unknown until the release of Trust No One. When connected with the machina fini mundi, it is what allows the machine to target subduction zones. In The Black Book of Buried Secrets, a code on page 31 reads, if cracked, 'protect golden ring.' On page 39 in the same book, it says, 'Keep Gideon's gold ring safe.' The back of the first cards in every Cahills vs Vespers book arranged in order forms a detailed diagram of the ring. In Day of Doom, the ring was taken from Amy and went into the Vesper's hands. When Gideon's ring was inserted into the device, it melts when the machine backfires. The ring was gone forever.
- Gideon's father
- Gideon Cahill
- Olivia Cahill
- Madeleine Cahill
- George S. Patton
- Grace Cahill
- Fiske Cahill
- Grace Cahill
- Amy Cahill
- Damien Vesper III
- Damien Vesper didn't know much about the ring but he suspected its power and tried to obtain it several times.
- The only person, besides Gideon himself, who knew about the ring's secrets was Gideon's wife, Olivia. She kept the ring safe until her death.
- The ring was then passed down from generation to generation.
- The ring, however, at some point, was lost until it found its way to a bar in Casablanca which was found by George S. Patton, but was stolen by Grace Cahill, and for the next few years, has been in a chalet in the Swiss Alps until Amy Cahill has taken custody of it.
- Its former location was in Amy's custom-made Swiss Army Watch. It is believed there is a code on the ring that will help bring the downfall of the Vespers. The Vespers were given it by Amy and Dan in the book, Trust No One.
- On one of the pages of Vespers Rising, near what seems to be an arrowhead, are the phases of the moon.
- There are the phases of the moon and symbols of constellations hidden inside of it.
- Its first keeper was Mr. Cahill.
- In relevance to the Jefferson Puzzle, all of the cards of Cahill vs. Vespers Card Pack 1 and Card Pack 2's backs are part of the puzzle. It forms a cross (like on ambulances) but in the center 6 cards are missing. The 6 missing parts of the puzzle represent the 6 books of Cahills vs. Vespers. The first card in each set of cards that come in the books make a grid, showing a diagram that resembles an X-ray of Gideon's ring.
- It is revealed the ring is the final piece to finish the "Machina Fini Mundi " machine for the end of the world AKA the doomsday device.