|Leader(s)||Vikram Kabra, Bae Oh, Ivan Kliester, Cora Wizard, Unknown|
|Goal||Collect the 39 Clues to unlock the master DNA serum, stop the Vespers|
|Enemies||Law enforcement officers, Vespers|
The Cahill family is the most influential family in the history of the planet. There are five branches, each from a child of Olivia Cahill. The family has a powerful secret that can be reached with 39 Clues across the globe. Each Cahill branch has a different personality based on the founding members of the branches.
The first known Cahills were Gideon Cahill (born in 1460), and his wife, Olivia Cahill (born in 1464), together, they had four children. Luke in 1484, Katherine in 1492, Thomas in 1494, and lastly, Jane in 1497. They lived happily on an island off the coast of Ireland, and Gideon worked on a cure to the plague. He created a cure with 39 different items. He gave a fourth to his children, but a side-effect was it effected their DNA. Gideon frequently invited Damian Vesper to the island, but one day the Vespers set fire to his house, betraying them.
Gideon died, and the others survived, and blamed Luke for the disaster. Luke was outraged and split from the other three, and Jane ran away in shock. Katherine and Thomas went off together, but three years later Katherine would betray Thomas. This is how the Ekaterina, Tomas, Janus, and Lucian branches were formed. Olivia was pregnant with Gideon's third child, Madeline Cahill. She founded the Madrigal branch, and they tried to keep the Clues from being assembled, and protect the Vesper ring.
The Cahills quickly rose to be the most expansive and influential families ever. With their altered DNA, they became famous for their talents, and also searched for the Clues. The Cahill branches always fought each other, but the Madrigals were trying to re-unite them. The Madrigals always tried to re-unite the branches to fight the Vespers. The Vespers however were doing the opposite, creating discord.
When Grace Cahill died, all Cahills were sent into a hunt for the 39 Clues. However it was actually the Madrigal master plan. Amy Cahill and Dan Cahill were sent into the race to find clues unaware of their heritage. With one member of each branch participating, Amy and Dan were presented their task by Fiske Cahill. They went with a member of each branch in the Madrigal gauntlet and united the branches against Isabel Kabra. But was it enough to get unity against the Vesper threat?
Grace's hunt for the Clues had been recorded by a team of agents, Rick Riordan, Gordan Korman, Peter Lerangis, Jude Watson, Patrick Carman, Linda Sue Park, and Margaret Peterson Haddix. They sold their records of the events as child's fiction, but it told the world about the Cahills and Vespers. With the aid of Tomas online gamers, they created a Black Book containing the secrets of each branch.
- Olivia Cahill
- Gideon Cahill
- All Ekats
- All Tomas
- All Lucians
- All Janus
- All Madrigals