The reason that mysterious Alex (Albert Dupontel) works for a low wage at the armored transport company (and lives in a hotel that costs more than he earns) is because he is a former banker and a witness of a previous attack on a cash truck, in which the robbers killed his son and almost him. He thinks there is a plant, and wants to find out who. The plant is Jacques "Jackpot" (Jean Dujardin). With him, the gangsters manage to break into the company and almost all the drivers get killed.
However Alex is able to overpower Jacques, and all the gangsters get killed. Jacques is locked by Alex in the room with the money; the female driver (Claude Perron) is able to escape, and Alex leaves, however he seemingly dies of his wounds at the place his son was killed.