It takes a lot of nerve to assume such a thankless (an euphemism) part ;Vincent Macaigne (who played his game well in the average comedy "Des Plans Sur La Comète" ) is an actor to be taken seriously and he's not about to succumb to the "feel good" atmosphere which mars the contemporary French scene .
Either this hero is a meek saint or he takes masochism to new limits ; it may be another (how ironical !) story of the living being (man or dog ,it does not seem to matter anymore in that context ),who after an eventful journey ,a la "Lassie " comes back to his sweet home ..If Lassie were a man...
Our hero loses his wife (Vanessa Paradis ,whose part is almost a cameo ,his job, everything ) He is ridiculed (the bank executive) and treated with suspicion and contempt by his former boss .He seems divorced from the realities of this world : if it were not so,how could he pay such a price to the pet shop man ?When the dog he just bought gets run over , training lessons for dogs he bought from the dubious man is all he has left ;as he 's got no dog anymore ,he will be the dog.Much to the pet shop guy's surprise, he comes for the training .
Never the sentence "he's treated like a dog" had made such sense: humiliation,S/M games , bondage,homosexuality (and however this is not a gay porno movie) abound ; there's more to the picture than meets the eye : what is the dog/man searching? love,tenderness, or merely a place in this world.
You can interpret this fable according to your own sensitiveness; it may be a metaphor for our world ,where only the strong survives ;the story of an extreme masochist ; the longing for a square deal for the human (?) being ; the legitimate desire to find back ,whatever the cost , your family .
As French connoisseur "search and destroy" warned you,definitely a film only suitable for an informed audience ,not for squeamish .
In the years to come,Vincent Macaigne will be a name to reckon with.