| Dean | Acheson | Under Secretary. |
| Harold | Agnew | A graduate student. |
| Samuel | Allison | Los Alamos's director. |
| Luis | Alvarez | A rad lab recruit. |
| Walter | Alvarez | Mayo Clinic physician. |
| Don Diego | Arias de Quiros | Spanish conquistador. |
| Whitney | Ashbridge | Groves's new CO. |
| Bob | Bacher | A rad lab recruit. |
| Jean | Bacher | Bob's wife. |
| Kenneth | Bainbridge | A rad lab recruit. |
| Jim | Baker | Bohr's son AKA: Aage. |
| Ralph | Bard | Under Secretary of the Navy. |
| Henry | Barnett | Helpmann's recruit and former classmate. |
| Shirley | Barnett | Henry's wife. |
| Isabel | Bemis | Condon's assistant. |
| Hans | Bethe | One of Oppenheimer's colleagues. |
| Rose | Bethe | Hans's wife. |
| Alide | Bigelow | Dorothy's old classmate. |
| Felix | Bloch | A Swiss-born theoretician. |
| George | Bloom | President of the first National Bank. Dorothy's friend. |
| Niels | Bohr | Father of Quantum Physics. AKA: Nicholas Baker. |
| Gregory | Breit | Oppenheimer's predecessor. |
| James | Byrnes | Secretary of State. |
| Smitty | Carlisle | The post's lawyer. |
| James | Chadwick | Discoverer of the Neutron. |
| Lord | Cherwell | Churchill Scientific Advisor. |
| Peggy Pond | Church | Dorothy's friend. A Santa Fe writer. |
| William | Clayton | Assistant secretary of the State. |
| Roy | Cohn | Prosecution aide. |
| Arthur | Compton | Director of the MET Lab. |
| Dr. | Conant | Groves's technical adviser and liaison. |
| James | Conant | Groves's primary Science advisor. |
| Edward | Condon | Personnel manager. |
| Charles | Critchfield | Oppenheimer's new recruit. |
| Paul | Crouch | Sylvia's husband. |
| Sylvia | Crouch | Former Officer of the American Communist Party. |
| Harry | Daghlian | Los Alamos's first casualty. |
| Joseph | Dallet | Kitty's ex-husband. |
| Frederic | de Hoffman | A Harvard physicist who joined the team. |
| Peer | de Silva | Los Alamos's security officer. |
| David | Dow | Bacher's brother-in-law. |
| Daniel | Drake | A leading Cincinnati physician. |
| | Dudley | Colonel. |
| Brian Boru | Dunne | A town reporter. |
| George | Eltenton | British engineer. |
| Thomas | Farrell | Deputy Military Commander of the Manhattan Project. |
| Enrico | Fermi | A nobel prize-winning Italian physicist. |
| Martha | Field | The owner of the building at 109 East Palace. |
| Leon | Fisher | One of the recruits. |
| Leon | Fisher | A physicist. Phyllis's husband. |
| Phyllis | Fisher | Leon's wife. |
| Cecil | Frey | An old-time rancher. |
| Otto | Frisch | The man who proposed an extremely bold experiment. |
| Klaus | Fuchs | A German member of the mission. |
| Harry | Gold | An American courier. |
| Priscilla | Greene | Oppenheimer's secretary. |
| Eleanor | Gregg | Dorothy's friend. A Santa Fe writer. |
| Leslie | Groves | A professional soldier and trained engineer. Oppenheimer's boss. |
| Payk | Hagemann | Helpmann's recruit and former classmate. |
| Marjorie | Hall | Bradner's wife. |
| George | Harrison | Stimson's special advisor. |
| Richard Stewart | Harrison | Kittty's second husband. |
| Will | Harrison | Editor of the Santa Fe New Mexican. |
| Louis | Hempelmann | The project's medical director. |
| Alice Corbin | Henderson | A Sunmount patient. |
| William Penhalow | Hern | Painter. Alice's husband. |
| Bourke | Hickenlooper | A senator. |
| Herbert | Hoover | A colonel in World War I. Stimson's superior. |
| J. Edgar | Hoover | FBI director. |
| Jack | Hubbard | A meteorologist. |
| Bill | Hudgins | One of the project's new hires. |
| Robert | Hutchins | President of the University of Chicago. |
| Lyall | Johnson | The local chief. |
| Wilhelm | Keitel | Chief of Staff of the Wermacht. |
| George | Kistiakowsky | A Harvard chemist. |
| John | Lansdale | Pentagon chief. |
| William | Laurence | A New York Times reporter. |
| Ernest | Lawrence | The inventor of Cyclotron. |
| Rossi | Lomanitz | One of Oppenheimer's physicists. |
| Barbara | Long | A popular Science teacher. |
| Edwin | Macmillan | One of Lawrence's proteges. |
| John | Manley | An experimental physicist. |
| Frances | Margaret | Dorothy's sister. |
| Herb | Marks | Oppenheimer's lawyer. |
| Herbert | Marks | Acheson's legal aide. |
| George | Marshall | One of the committees. |
| Anita | Martinez | Dorothy's recruit. |
| Maria | Martinez | Anita's mother-in-law. New Mexican pueblo artist. |
| Joseph | McCarthy | A senator. |
| Joseph | McKibbin | Dorothy's husband. |
| Kevin | McKibbin | Dorothy's son. |
| Ed | McMillan | A rad lab recruit. |
| Elsie | McMillan | Ed's wife. |
| John Gaw | Meem | Architect. Katherine's mentor. |
| Frank | Mera | Sunmount director. |
| Harry | Mera | Frank's brother. |
| Robert | Milikan | A nobel prize-winning physicist. |
| Emily | Morrison | Phil's wife. |
| Duane | Muncy | Business manager of the new housing project. |
| | Neddermeyer | The new Division Head. |
| Steve | Nelson | Dallet's close friend. |
| | Nichols | Groves's colonel. |
| James | Nolan | Helpmann's recruit and former classmate. |
| Jean | O'leary | Groves's administrative assistant. |
| Frank | Oppenheimer | Oppenheimer's brother. |
| J. Robert | Oppenheimer | Head of the Manhattan Project. AKA: Mr. Bradley, Oppie. |
| Julius | Oppenheimer | Oppenheimer's father. |
| Peter | Oppenheimer | Oppenheimer's son. |
| Miguel | Otero Jr | Katherine's husband. |
| T.O. | Palmer | SED's new CO. |
| Deke | Parsons | Oppenheimer's boss. |
| Colonel | Pash | Eltenton superior. |
| Robert | Patterson | Under Secretary of War. |
| Bernard | Peters | Oppenheimer's talented former student. |
| Harriet | Peterson | A red-headed nurse at Los Alamos. AKA: Petey. |
| Kitty | Puening | Oppenheimer's wife. |
| Elinor | Pulitzer | Hempelmann's girlfriend. |
| Isidor | Rabi | One of Oppenheimer's men. |
| Norman | Ramsey | A rad lab recruit. |
| Roger | Robb | AEC attorney. |
| Jane | Roberg | A physicist who worked on calculations for the fusion weapon. |
| Franklin | Roosevelt | The current US President. |
| Arthur | Ryder | The Chairman of the Sanskrit Department. |
| Frances Davis | Scarritt | Dorothy's mother. |
| Jim | Scarritt | Dorothy's nephew. |
| Reverend | Scarritt | Dorothy's well-known ancestor. |
| Virginia | Scarritt | Dorothy's sister. |
| William Chick | Scarritt | Dorothy's father. |
| Dorothy Ann | Scarritt-McKibbin | The woman who ran the project at 109 East Palace Avenue. Protagonist. |
| Emilio | Segre | An Italian physicist who escaped Mussolini's regime. |
| Robert | Serber | Oppenheimer's protégé. Los Alamos director. |
| Charlotte | Serbert | Serber's wife. |
| Joseph Henry | Sharpe | Western painter. |
| Herbert | Smith | Oppenheimer's old teacher. |
| Joe | Stevenson | A local entrepreneur. |
| Henry | Stimson | Secretary of War. |
| Katherine | Stinson | A celebrity. Dorothy's friend. |
| Leo | Szilard | A Hungarian physicist and inventor. |
| Jean | Tatlock | Oppenheimer's former fiancé. |
| Jean | Tatlock | Serber's long-time girlfriend. |
| Edward | Teller | A Hungarian physicist. |
| Harry | Truman | The current US President. |
| Jim | Tuck | A member of the British Mission. |
| Gerald | Tyler | New Commanding officer. |
| Stan | Ulam | A Polish mathematician. |
| Harold | Urey | Los Alamos University Principal. |
| Joe | Volpe | Mark's partner. |
| Edith | Warner | Station's mistress. |
| Vera | Williams | John's wife. |
| Anne | Wilson | Groves's assistant. |
| Anne | Wilson | Oppenheimer's secretary. |
| Bob | Wilson | The first elected chairman. |
| Beverly | | Agnew's wife. |
| Helen | | Sam Allison's wife. |
| Lamy | | The archbishop. |
| Timoshenko | | Petey's dog. |