Reagan Holt is the twin sister of Madison Holt.
Reagan and Madison were twins to Eisenhower, and Mary-Todd Holt. They had an older brother, Hamilton, and they were Tomas. The Holts always went to Grace Cahill's week-long winter holiday at the Cahill estate. They grew to dislike many of the Cahill family. At school, Reagan played dodgeball and gave a student a concussion, and kicked students. Reagan signed up for a new Kickboxing PE elective, and also went on a trip to Monument Valley, seeing the world's largest ball of twine.
After Grace died, the Holts came to her funeral, and Reagan and Madison held Dan Cahill upside down before dropping him, and insulting his tounge-tied sister, Amy Cahill. Reagan put a shovel of dirt on Grace's grave, and then the entire Holt family was invited to the will reading. William McIntyre played a video of Grace saying the Cahill's were a family with many famous people, and the Holt twins named people like Harry Houdini, who William confirmed were Cahills. Grace gave them the option to take a million individually or start the hunt for the 39 Clues. After Ian, and Natalie Kabra joined as Team One, the Holts protested they should be team one, and entered the hunt. They got a clue card with RESOLUTION and Richard S___ on it. Soon the Holt family left the mansion, but turned around to tail Amy and Dan in the library. Reagan and Madison jogged in place while Hamilton tried to smoke them out, but the whole mansion burnt down.
They followed Amy and Dan, setting a charge in the museum, but it was triggered by Sinead, Ned, and Ted Starling instead. The Holts flew to Pairs and knocked out Alistair Oh, taking the Poor Richard's Almanack. They looked at it, seeing writing by Hope Cahill talking about the Maze of Bones, but Irina Spasky stole it. Angry, the Holts got a rental car, but drove it in Seine, and then got an ice cream van, and wire-tapped the Lucian stronghold in Pairs. As they were going to begin the assault, Amy and Dan slipped in, and the Holts thought they took the Almanack. Reagan was fighting Arnold over ice cream when Eisenhower formed the Holts up, citing previous failures as the drive to crush them now. Reagan said that the Starlings might be dead, but Eisenhower scolded her for going soft.
At the Île Saint-Louis, the Holts stood over Amy and Dan trapped in a bit, thinking that they'd found the Maze of Bones. With shock, the Holts revealed that they had attacked them twice before. When the cement truck arrived with thugs ready to bury Amy and Dan, Reagan wanted to help, but couldn't. Eisenhower pulled them out, thinking Amy knew the Clue, and the Holts attacked. Madison and Reagan hit a thug across the street into a flower shop window. Reagan was knocked out with a concussive grenade meant for two thugs along with her family. They drove to the St. Pierre de Montmarte church, and Reagan used frozen ice cream as ammunition, following Amy and Dan up to the belfry. When her dad was going to crush Amy and Dan, Reagan asked why the police were here, causing the Holts to flee.
They waited in Dijon, France for Amy and Dan's train, Madison commenting her hamburger had to much mustard, and Reagan explained Dijon's the mustard capital of the world, earning a punch from Madison. When the train arrived, the Holts snuck on and followed Amy and Dan into a mail room where the twins held them up. Eisenhower began to strangle Dan when Amy lied about the KV 617 music sheet. Amy showed them the overhead where it was, only shredded by Saladin. Questioned if they had tickets, the Holts jumped from the train.