Joyeux demiversaire! - Oeuf dur ou oeuf doux

The OSI offices are haunted by a ghost and the agents have to do sums to get rid of it. Omar and Ozlyn, a new recruit, must feed a creature by measuring liters.

Otis and Olympia carry out a mission within a specific budget. Otis must find a wrong-doer using his numerical ruler.

OSI uses symmetry to solve a problem. Olympia is trying to recover a stolen gadget and has to measure the temperature of different liquids.

Olympia must measure different temperatures to stop competing with the new agent named Olympia. Otis and Olympia distinguish between adding and multiplying zero.

Oona, Olympia and Otis accidentally alter the past, and all the investigations carried out and solved by the OSI have to start again from scratch.

Oona, Olympia and Otis accidentally alter the past and must solve numerical and non-numerical sequences to return to the present.

Olympia and Otis use a Venn diagram to negotiate a deal between two enemies. A team consults a map to navigate the corridors of OSI while Mrs. O is away.

To keep Agent Orson from being evicted, Otis and Olympia use pie charts and Venn diagrams to help him. Oona transports herself to a parallel universe and plays with numbers to get back to the real world.

Olympia finds regularities using a data table to solve problems. She discovers Otis's childhood secret.

Otis, Mrs. O, Olympia and Oona use a broken-line diagram and a numerical right to fight a common enemy.