| Marcel | Allan | One of the apprentices. |
| Dora | Armstrong | One of the apprentices. |
| Ned | Asbrey | One of the apprentices. |
| Uday | Bal | The department head and principal engineer. |
| Heather | Baxter | One of the apprentices. |
| Mary Hayley | Bell | English actress, writer and dramatis. aka: Lady Mills. |
| Nancy | Brickett | Director and founder of the Secondhand Book and Curiosities. |
| Johnny | Cash | American singer, songwriter, musician, and actor. |
| Patrick | Castle | A third-year apprentice. |
| George | Cavendish | A field marshal for the British Army. |
| Winston | Churchill | British Prime Minister. |
| Preston | Dinn | A Ghanaian immigrant and first-year apprentice. |
| Porter Lynn | Duong | An American actress. |
| David | Eston | Marion's fellow first-year apprentice. |
| Michael | Evans | A Cardiology Specialist. |
| Maud | Finkle | One of the apprentices. |
| Dr. | Fitzpatrick | The medical head. |
| Henry | Gillroth | The head of Human Resources and High Council member. |
| Verity | Gould | One of a senior Inquirers. |
| Karthy | Govender | South African human rights commissioner and academic. |
| Reginald | Grunstone | Marion's cousin. |
| Dolores | Hacksworth | Marion's grandmother. |
| William | Hobb | Marion's partner in the clockwork bird project. aka: Bill. |
| Jane | Holland | A six-year-old girl who went missing on her way home. |
| Kenny | Hugo | The newly inducted private detective from New York. |
| Helena | Jansen | A person who can make a clockwork safe. |
| Jessica | Meel | One of the bookshop apprentices. |
| Jessica | Meel | One of the apprentices. aka: Jess. |
| Rupert | Nicholas | The head of Miss Brickett's security. |
| John | Perry | Michelle White's colleague. |
| Aida | Rakes | A senior Inquirer and head of the Intelligence Department. |
| Constable | Redding | A police officer. |
| Amanda | Shirley | The seventh and oldest first-year apprentice in Marion's group. |
| Don | Shu | One of a senior Inquirers. |
| Barbara | Simpkins | An employee assigned in the library. |
| Mr. | Smithers | Marion's acquaintance. |
| Delia | Spragg | An agency tailor and council secretary. |
| Frank | Stone | A recruitment officer for the bookshop. |
| Edgar | Swindlehursrt | One who had the most brilliant minds at the agency. |
| Norman | Tucker | An English musician, administrator and translator. |
| Michelle | White | An Inquirer. |
| Howard | Yon | Patrick's friend and a fellow third-year apprentice. |
| Alice | | Marion's mother. |
| Erin | | Reginald's wife. |
| Felix | | Owner of an auto repair shop. |
| Harry | | Miss Brickett's employee. |
| Mae | | Frank's sister. |
| Marion | | An apprentice at Miss Brickett's Secondhand Book and Curiosities |
| Roger | | A maintenance. |
| Thomson | | One of a former Inquirers and trained acrobats. |
| Thorpe | | One of a former Inquirers and trained acrobats. |
| Toby | | Mr. Nicholas' snake. |
