It’s a pain that Sigmund (Anthony Hopkins) medicates with morphine, the drug he would use to end his life a mere three weeks after the action of this film, which opens with the doctor waking, in London, from a dream of the Nazi-occupied Austria he fled a year and a half earlier. England has just entered World War II. Air raid sirens will soon punctuate the backdrop.

So it’s a little odd when Matthew Goode’s Lewis, who goes by Jack, shows up in this un-relaxing setting, by invitation, for a light chat over whiskey about faith and doubt and good and evil — and with sexuality thrown in for giggles. Hopkins’s Sigmund, still frisky, apparently finds a balm of sorts in such intellectual debate, which he admits to having been spurred to after reading Lewis’s “The Pilgrim’s Regress.” The 1933 allegorical novel includes a character called Sigismund Enlightenment, a “vain and ignorant old man” said to have been based on Freud.

Viewers of “Session” may find it harder to take solace from (or to find entertainment in) this stagy jar of slightly pickled discord, directed by Matt Brown, based on the 2011 play by Mark St. Germain (itself inspired by Armand Nicholi’s 2002 book “The Question of God”).

To be sure, Hopkins delivers a lively performance, with Goode suffering from the limitations of Brown and St. Germain’s script, under which Jack is little more than a mouse being toyed with by Sigmund’s catlike arguments and intellect. The film’s roots as a stage-bound two-hander are hard for Brown to transplant to the screen, despite numerous flashbacks to Sigmund’s childhood, where his Catholic nanny runs afoul of the boy’s Jewish father, and to Jack’s World War I service, during which he promises a doomed comrade to look after the dying soldier’s mother, should any dire fate befall him.

Another side plot — more distracting than diverting — involves Anna Freud (Liv Lisa Fries), Sigmund’s psychoanalyst daughter, who is shown rushing around London trying to refill her father’s morphine prescription even as she summons the courage to confess her love for Dorothy Burlingham (Jodi Balfour), a fellow psychoanalyst, to her father. It’s a lot in a small movie that strains at the seams to contain all this in a single day.

There are some heady pleasures. After Jack arrives, and is warned off sitting in what Sigmund calls the “transformation couch,” a place of honor for so many of his patients, the famous shrink proceeds to open up Jack’s head and look inside. (Sigmund makes a veiled reference or two to the bachelor Jack’s somewhat ambiguous sexuality, and whether he lives with a woman — or man. Not that there’s anything wrong with that, Sigmund adds, in effect.)

It is perhaps more accurate to say that the two men put each other on the couch, ultimately trying to peer inside each other’s crania, poking and probing without really provoking any actual insight, in a film that looks as drab and gray as it sounds. “I consider what people tell me less fascinating than what they choose not to tell me,” Sigmund says, as one might expect him to.

In the end, the dueling protagonists of “Freud’s Last Session” arrive at something of a stalemate. “One of us is the fool,” Sigmund says, of the questions that lie at the heart of the film: Does God exist? And if so, why could such a creator allow evil? Is the latter proof or negation of the former?

“If you’re right, you won’t be able to tell me so,” Sigmund continues, presumably referring to the finality of death. “And if I’m right, no one will ever know.”

That, at least, is one sure thing, in a film whose intriguing ideas are made stale and unsatisfying by their dull and dutiful delivery. “Freud’s Last Session” ends with Sigmund restocked with painkillers, and Jack on the train back to Oxford, his head still free of (or perhaps fuller than ever with) doubts. Who knows whether either man — or the viewer — has been changed?

The final shot is a nice and artful one, in a film that lacks more of them. The camera lingers on the dark tracks ahead, only a few feet of which can be seen, illuminated by the headlight of the engine. It hurtles on into the night, heedless of what is not, and cannot be, known.

PG-13. At area theaters. Contains mature thematic material, some bloody, violent images, sexuality and smoking. 108 minutes.