The first book in the series The 39 Clues
, Rick Riordan’s novel The Maze of Bones
(2008) begins the adventures of Amy and Dan Cahill, a pair of orphans who discover, after their grandmother's death, that they belong to a long, secretive, and powerful lineage. They are members of the Cahill family, which includes many of the most famous and accomplished humans in history. It also includes many of the most dangerous: the myriad members of the Cahill family are locked in a deadly internal feud to discover the ingredients to a powerful serum that only they know about.
Just before Grace Cahill, the matriarch of the Cahill family dies, she beckons her lawyer to her bedside and dictates a change to her will. No sooner does she die, then from out of the nearby shadows steps a man dressed in black, who consults quietly with her lawyer, William McIntyre.
Grace's grandchildren, Amy and Dan Cahill, are on their way to their grandmother's mansion, where her funeral is being held. Traveling with them is their guardian, their Aunt Beatrice. Just before the funeral, they have a run-in with their distant relatives, the Holt family: Eisenhower and Mary-Todd, and their three children, Hamilton, Madison, and Reagan. It doesn't go well. At the funeral, some of the extended Cahill family is called into a separate room for the will reading. Besides Amy and Dan, these include the Holts, the Kabras family, Alistair Oh, Ian and Natalie, ex-KGB agent Irina Spasky, famous rapper and TV show host Jonah Wizard, the Starling Triplets, and Aunts Beatrice and Ingrid. Grace's lawyer shows them a video she recorded before she died. In the video, Grace tells the selected Cahills that they have a serious decision to make – it will be the greatest challenge any of them have yet faced. The decision? They may either take one million dollars, no questions asked, or receive a chance to solve a mystery and become the greatest of all the Cahills. They are told they have exactly five minutes to decide.
At first, Dan wants to take the money, which he dreams of spending on baseball cards. Amy, however, encourages him to consider the chance to become the greatest of the Cahills. She wants to do what she thinks her grandmother would have wanted. The Kabras family attempts to intervene, trying to persuade
Dan and Amy to just take the money. Mr. McIntyre explains to the children how many famous people were Cahills: Abraham Lincoln, Harry Houdini, explorers Lewis and Clark – and many others. In the end, the siblings choose to forgo the money. The Kabras, the Holts, Irina Spasky and Alistair Oh also accept the challenge. In return, they are handed a mysterious envelope. Inside, it reads, "Resolution: The fine print to guess. Seek out Richard S." Everyone but Amy and Dan leaves, and while the siblings ponder the clue, McIntyre relays a special warning from Grace to “beware the Madrigals.”
Amy investigates Grace's library but fails to find anything useful. Dan, however, finds a secret passage leading to another, secret study where the siblings and Alistair find Grace's copy of Poor Richard's Almanac
. Before they have a chance to look at it closely, however, they realize that the mansion is on fire, and they are in danger. The children escape through the vent system and make their way home with the help of their au pair, Nellie. The next location of their search is the Franklin Institute, which is also subject to mysterious destruction during their visit – it collapses, injuring the Starling triplets, but Amy and Dan survive. The siblings find out that Irina Spasky is now in possession of the Almanac, and begin tailing her to get it back. Irina leads the children to an island, where she has laid a trap for them, but at the last minute, they are saved, quite unexpectedly, by the Holts. Afterward, they divulge the true scope of their search to Nellie, who agrees to help them find all thirty-nine clues.
The siblings' next stop is Paris, specifically, the Paris catacombs. They solve several puzzles there – left behind by famed Cahill Benjamin Franklin, the destruction of whose institute they earlier escaped – which lead them to the location of the next clue: a church containing an unusual mural. The mural depicts the four original Cahills – Katherine, Tom, Luke, and Jane, after whom the current four branches of the family are named. In the room, they find a small bottle with writing all over it. Dan decodes the writing, and Amy attaches the phial to a lightning rod designed by Benjamin Franklin. This seems to charge the phial, but before the siblings can do anything with it, the Kabras steal it. However, Dan still has the slip of paper that had been attached to the bottle, which contains a puzzle that the children decode. The answer to the puzzle is the next ingredient of the serum: iron solute. Amy does further research on Benjamin Franklin, which suggests that the next clue will be located in Vienna, Austria.