Many folks who watch this film today might be a bit confused about the context, so I'll try to explain. When the Spanish Republican army was defeated by Francisco Franco's troops at the end of the Spanish Civil War in the late 1930s, many Republicans (many of whom were communists and socialists) were jailed or killed--and many more poured over the border into exile in countries like France.
The character Yves Montand plays in this film, Diego Mora, is one of these communist exiles--one who regularly sneaks back and forth between the countries on missions for his cause. Exactly what he does on these missions is never talked about very much in these films but he and his comrades are trying to keep alive a small dissident group within Spain. However, during one of these many trips, he is taken in for questioning at the border. Somehow the police have become suspicious but with the help of a young French lady (Genevieve Bujold) he's able to extricate himself from custody. But, others in the organization weren't so lucky and were arrested. Because of this, Mora plans on returning to Spain to try to alert others in his cell so they can escape. However, instead of doing this, he spends so much of the film doing nothing in particular. In fact, that is a HUGE problem with the film. He learns about the possible leak in his organization and the arrests early on in the film and yet doesn't return to help the other agents until about 90 minutes later. In the interim, he meets with several women he cares about or wishes to have sex* with before his return to Spain. In addition, he talks and talks and talks--too much to keep the film interesting or well-paced. Overall, an interesting and well acted curio--especially since Montand himself was a communist and much of the story seems ironic in light of his own background as an Italian expatriate. But not a particularly enjoyable curio.
*Oddly, the first sex scene in the film was one of the most unintentionally funny I have ever seen. Instead of showing any real skin, the camera kept showing everything BUT--and with all sorts of artsy angles and composition. It made me laugh and seemed bizarre in light of the very ordinary and non-prudish sex scene later in the film. Why they did this, I have no idea. Perhaps the first nude scene (with Bujold) was done this way because she was uncomfortable with nudity and I'd sure love to know why they handled it in such a silly manner.