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The 39 Clues Wiki

Gideon Cahill was the founder of the Cahill Family.


Gideon Cahill was the Cahill to invent the master serum. He is the father of Luke, Katherine, Thomas, Jane, and Madeleine Cahill. Damien Vesper (Damien Vesper is a Vesper) was Gideon's friend before 1507. In 1497, they were celebrating a Christmas feast when Gideon dared to correct him on a point of astronomy. After the feast, the two of them talked deeply about the point. In 1507, Gideon drank the Master serum, which was not perfected by the Madrigal Serum.


Vespers Rising[]

Part One - Gideon Cahill[]

He first appears in Damien Vesper's house, when Damien demanded to know what he had found. Unbeknownst to Gideon, Damien had planted a spy, Maria the house lady, to spy on Gideon's household to keep track of his research. Then when Gideon refuses to tell him what he found, he tries to kill Gideon by dropping the roof on him, however Gideon pushes the ceiling aside, and he pins Damien to the wall and demands why Damien tried to kill him. Then Damien's servant Balthazar comes in, and then Gideon leaves. He gave Luke, Katherine, Thomas, and Jane a part of that unperfected serum, each, after the fallout with Damien Vesper. During the fallout Gideon used the powers granted by the serum, and realized the serum would kill him, unless he made it perfect. Gideon was killed in a fire soon after, which everyone else thought was set on purpose, by their brother Luke, which lead his children scattering around the world, and founding the branches of the Cahill family. The actual reason for the fire was Damien Vesper, although Gideon technically started it (to save his family/stop Damien). Nobody knew his wife, Olivia was pregnant with Madeleine Cahill at the time. He also possessed a golden ring, also known as Gideon's Ring. He died before he knew Madeleine was alive.


Gideon Cahill's hair is described in Vespers Rising as a swirl of wild gray tufts like a bank of storm clouds. His rugged face was darkened from years of working in a laboratory. Chemicals had turned his frock into a palette of stains, and his forearms were covered with notes in Latin - notes he wrote when he couldn't find pieces of parchment. Gideon's gold ring, according to Damien Vesper, marked him as a man of worth. His eyes were fierce and bright under bushy gray brows, too.


  • Madeleine

    Madeleine Cahill, his daughter

    Jane Cahill - Daughter (deceased)
  • Louisa - Daughter-in-law (deceased)
  • ??? - Mother (Lived in Milan, deceased)
  • ??? - Brother (Lived in Dublin, deceased)
  • Mary Arden - Granddaughter (deceased)
  • Keiko - Daughter-in-law (deceased)


At one point of his life, Gideon received a golden ring which is revealed to possess incredible power, like the Master Serum. 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. It is now in Amy's custom-made watch.