Hamilton "Hammy" Holt is one of the Tomas Holt family.
Hamilton was born to Eisenhower and Mary-Todd Holt. He started to play football, and became a pretty good player at the trade. He soon had twin younger sisters, Reagan Holt and Madison Holt. They went to Grace Cahill's winter holiday week, meeting Amy Cahill, and Dan Cahill, taunting the 'losers'. At school, Hamilton signed up for Parkour lessons as an extended PE class. In August the Holts went to Monument Valley where Hamilton suspected his Dad disabled the delete function on his trip blog. They visited the world's largest ball of twine.
After Grace had passed away, the Holts went to her funeral. When Reagan and Madison held Dan upside down, Hamilton taunted Dan that the estate would be his. Hamilton put a shovel of dirt on Grace's grave, and the Holts were invited to the will reading where a video of Grace was played by William McIntyre, showing them Grace. She presented the option to take a million, or start the 39 Clues hunt. The Holts chose to join after Ian and Natalie Kabra become Team One, saying they're the best. They got a clue card, formed up, and left, but secretly followed Amy and Dan. When they didn't leave the library, Hamilton tried to smoke them out, and the mansion burnt down. They followed Amy and Dan still, to the Philadelphia Science Museum, where they set a concussive charge that exploded the museum, but failed to get Amy and Dan.
They flew to Pairs, where they ambushed Alistair Oh, taking the copy of Poor Richard's Almanack from him, though it was stolen by Irina Spasky. They got a rental car, but drove it in the Seine. Fed up with failure, the Holts decided to get an ice cream truck and raid the Lucian stronghold, but Amy and Dan slipped in first, and Eisenhower told everyone they'd go to Île Saint-Louis to trail them. Hamilton and Madison then resumed fighting. At the isle, they found Amy and Dan trapped in a pit, Eisenhower asking if it was the Maze of Bones. A cement truck with thugs pulled up to bury Amy and Dan, and Eisenhower saved them, thinking they had a clue. Hamilton attacked a thug, but a grenade knocked him out. Now angry they drove to the St. Pierre de Montmarte church where Hamilton used frozen ice cream as ammunition and followed Amy and Dan to the belfry, but when Eisenhower was able to get there, the police arrived, and the Holts fled.
Realizing Amy and Dan had the Clue, the waited for their Vienna-bound train in Dijon, France by eating hamburgers. When it pulled up, the Holts snuck on, and then caused quite a commotion on the train. When Eisenhower tried to chase Amy and Dan, Nellie sat on him. Hamilton picked her up, and set her in seat. The Holts surrounded Amy and Dan, Amy beaning Eisenhower with a hockey stick. When the kids lied about the Clue, Eisenhower began to strangle Dan, but Amy showed them the Clue in the overhead. Saladin however, had shredded the Clue, and the Holts jumped out the train when questioned about their being on the train.