but what was that riot about, the one that allowed our hero and the safecracker to walk into the police station undetected? Who instigated such a widespread riot so suddenly in Paris?
It's about how audaciously you are carrying on in calm.
After Pierret (the hero) realizes that the corrupt cops have his wife in custody, he asks "How do we get in?" "Leave it to me," replies Sartet (the safecracker). There then follows a montage of scenes where they visit numerous criminal types (in a restaurant, at a campsite, a tunnel), and Sartet is clearly asking them for their help. I thought that they were going to work together to storm the station, but organizing a crime spree as a diversion was more surprising and a much better idea.