| 1 | | | The Secret Stealer |
| | Michelle | White | An Inquirer. |
| 2 | | | Number Sixteen Willow Street |
| | Marion | | An apprentice at Miss Brickett's Secondhand Book and Curiosities |
| | Alice | | Marion's mother. |
| | William | Hobb | Marion's partner in the clockwork bird project. aka: Bill. |
| | Nancy | Brickett | Director and founder of the Secondhand Book and Curiosities. |
| | Dolores | Hacksworth | Marion's grandmother. |
| | Mr. | Smithers | Marion's acquaintance. |
| | Jessica | Meel | One of the bookshop apprentices. |
| | Frank | Stone | A recruitment officer for the bookshop. |
| | Felix | | Owner of an auto repair shop. |
| 3 | | | The Other Miss Brickett's |
| | Rupert | Nicholas | The head of Miss Brickett's security. |
| | David | Eston | Marion's fellow first-year apprentice. |
| | Maud | Finkle | One of the apprentices. |
| | Jessica | Meel | One of the apprentices. aka: Jess. |
| | Preston | Dinn | A Ghanaian immigrant and first-year apprentice. |
| | Roger | | A maintenance. |
| | Verity | Gould | One of a senior Inquirers. |
| | Don | Shu | One of a senior Inquirers. |
| | Jane | Holland | A six-year-old girl who went missing on her way home. |
| 4 | | | In The Gadgetry Department |
| | Ned | Asbrey | One of the apprentices. |
| | Uday | Bal | The department head and principal engineer. |
| 5 | | | The Snitch |
| | Patrick | Castle | A third-year apprentice. |
| | Howard | Yon | Patrick's friend and a fellow third-year apprentice. |
| | Aida | Rakes | A senior Inquirer and head of the Intelligence Department. |
| | Barbara | Simpkins | An employee assigned in the library. |
| | Amanda | Shirley | The seventh and oldest first-year apprentice in Marion's group. |
| | Edgar | Swindlehursrt | One who had the most brilliant minds at the agency. |
| | Norman | Tucker | An English musician, administrator and translator. |
| | Constable | Redding | A police officer. |
| | John | Perry | Michelle White's colleague. |
| 9 | | | Bill's Secret |
| | Henry | Gillroth | The head of Human Resources and High Council member. |
| 10 | | | The Induction Ceremony |
| | Kenny | Hugo | The newly inducted private detective from New York. |
| | Dora | Armstrong | One of the apprentices. |
| | Marcel | Allan | One of the apprentices. |
| | Heather | Baxter | One of the apprentices. |
| | Mae | | Frank's sister. |
| 11 | | | Dolores Ultimatum |
| | Reginald | Grunstone | Marion's cousin. |
| | Erin | | Reginald's wife. |
| | Harry | | Miss Brickett's employee. |
| 12 | | | The Smoking Clock |
| | Delia | Spragg | An agency tailor and council secretary. |
| 16 | | | The Gray Eagle |
| | Thomson | | One of a former Inquirers and trained acrobats. |
| | Thorpe | | One of a former Inquirers and trained acrobats. |
| 17 | | | The Lie And The Tightwire |
| | Toby | | Mr. Nicholas' snake. |
| | Johnny | Cash | American singer, songwriter, musician, and actor. |
| | Porter Lynn | Duong | An American actress. |
| | Michael | Evans | A Cardiology Specialist. |
| | Karthy | Govender | South African human rights commissioner and academic. |
| | Mary Hayley | Bell | English actress, writer and dramatis. aka: Lady Mills. |
| 19 | | | The Seven-Year Safe |
| | Dr. | Fitzpatrick | The medical head. |
| | Helena | Jansen | A person who can make a clockwork safe. |
| 23 | | | The Legacy of Sir Cavendish |
| | George | Cavendish | A field
marshal for the British Army. |
| | Winston | Churchill | British Prime Minister. |
