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.