Mara, Joss and Nadir set off on an orienteering challenge on the desert plateau of Sarn. An arch seems to await them at the end of the wrong path. To find the three markers and return in time, their team will have to change both route and leader.
Léna has two days to disassemble the lens of an old lighthouse. Then a boat breaks against the island and the storm closes the return. To bring everyone back to port, she will have to leave behind more than a glass case.
Mandated to open a river connection, a cartographer discovers that his survey is interrupted before arrival. A flood, a damaged boat and a ceremony already announced transform the mission into an unexpected crossing.