As played by Benicio Del Toro — flattening vowels, biting at consonants, pushing his tall, square frame though postures of graceful anguish — Jimmy Picard, a World War II veteran and a member of the Blackfoot Indian tribe, is the picture of a noble soul in torment. He is both charismatic and pathetic, and he inspires in his therapist, a French anthropologist and psychoanalyst named Georges Devereux (Mathieu Amalric), a complex mixture of responses, including sympathy, rivalry and unabashed ethnographic curiosity.

Their relationship is at the center of “Jimmy P.: Psychotherapy of a Plains Indian,” Arnaud Desplechin’s ruminative, gentle and absorbing new film. Based on the writings of the real Georges Devereux about a real patient, Mr. Desplechin (who wrote the screenplay with Kent Jones and Julie Peyr) tells a story that both challenges conventional movie images of heroic (or diabolical) therapists and reasserts the value of old-fashioned, talk-based, dream-focused psychoanalysis.

Rather than present Jimmy’s symptoms — which include catatonic episodes and brutal headaches — as a puzzle to be solved, the film uses them as a springboard into the mystery of his personality. And while there is no magical, permanent cure in prospect, there is a sober, humane conviction that suffering can be diminished and life improved.