Injured while trying to prevent thieves from taking his goods, the irresponsible César Montesiho "borrows" the health insurance card of his old friend, Arthur Dreyfus, in order to have an x-ray without paying. The next day, the radiologist summons the latter, a researcher at the Institut Pasteur, to tell him that he has incurable lung cancer. In shock, Arthur doesn’t tell the doctor about the identity theft and then has to tell César the bad news. But he falters to the point that César believes Arthur is the one with the disease. This misunderstanding propels the two friends on a last-ditch trip, which leads them from Paris to Biarritz, then to India, where a revolutionary treatment may allegedly be found.