Roger, Romane's brother, has been transferred to an Algapower lab in Brazil. Shortly afterwards, his sister, still working for Intelligence, arrives in Rio. Her new mission: to get in touch with her brother and convince him to inform the authorities on the company and its mysterious Mermaid Project....

Roger, Romane's brother, has been transferred to an Algapower lab in Brazil. Shortly afterwards, his sister, still working for Intelligence, arrives in Rio. Her new mission: to get in touch with her brother and convince him to inform the authorities on the company and its mysterious Mermaid Project. The stakes have changed for the Pennac siblings, though: among the documents retrieved during the New York mission, their names appear on a list of potential test subjects...