| Pro | Benjamin | Daniels | Jess's half-brother. Missing. Aka: Ben. |
| | Jess | Hadley | Ben's half-sister. |
| | | | Novel |
| | Sophie | Meunier | One of Ben's neighbors. Jacques's wife. |
| | Benoit | | Sophie's silver whippet. |
| | David | Mallet | Sophie's hairdresser. |
| | Concierge | | The gatekeeper of the building. |
| | Mimi | | The girl who lived on the 4th floor. Aka: Mervielle. |
| | Monsieur | Gus | Mimi's old stuffed toy. |
| | Camille | | Mimi's flat mate. |
| | Theo | Mandelson | The Paris editor. |
| | Suki | | The cat. |
| | Nick | | Benjamin's friend and neighbor. Aka: Nicolas. |
| | Mr. | Anderson | Jess's fostered father. |
| | Antoine | | Ben's neighbor over at the 1st floor. |
| | Dominique | | Antoine's wife. |
| | Blanchot | | The police commissioner. |
| | Guy | | One of Nick's friends. |
| | Harry | | One of Nick's friends. |
| | Irina | | The mystery girl. |
| | Elira | | The concierge's daughter. |
| | Loulou | | Camille's friend. |
| | Victor | | The guy that Jess met at the party. |
| | Henri | | Mimi's art teacher. |
| | Paula | Rego | A visual artist. |