David Cronenberg’s A Dangerous Method may be the most boring sex dramedy ever made. Apparently intended as a provocative portrait of the rocky relationships between early psychoanalysts Carl Jung, Sigmund Freud and Sabina Spielrein, the film emerges instead as a strange blend of biopic conventions and bawdy humor.

From scene to scene, the movie shifts awkwardly between dry exchanges of dialogue and campy moments of theatrical comedy. Since Cronenberg and the cast refuse to commit to a consistent tone, none of these scenes amounts to anything more than a muddled mess.

A Dangerous Method endeavors to tell the story of the two most tumultuous relationships of Carl Jung’s career. Unfortunately, though, screenwriter Christopher Hampton does not split the film evenly between them. Instead, he chooses to focus the script’s attention mostly on the awkward association between Jung and Sabina Spielrein, who begins as Jung’s patient, only to later become his colleague and love interest. While this peculiar bond may have looked fascinating on paper, it falls completely flat on screen thanks to the terrible performances of Michael Fassbender as Jung and Keira Knightley as Spielrein. The two leads lack any semblance of chemistry, and their acting styles clash in virtually every scene of the film.

Whereas Fassbender relies on stiff and subdued manners of speech and movement to capture the apparent dullness of Jung, Knightley plays Spielrein as a shrill harpie with a laughably flimsy Russian accent. If Knightley had developed her overwrought portrayal a bit more, and if Fassbender had imbued his Jung with a sense of drama, the two characters might have created sparks, perhaps even some laughter. As it is, however, the two never connect with each other or with the audience, and their conversations about sexuality come across as remarkably un-sexy.

In fact, the only real sexual tension in the film arises between Jung and Viggo Mortensen’s Freud. Jung’s discipleship of and devotion to Freud never lead to overt romance, but the arc of the two men’s relationship in the film takes the form of a conventional love affair, beginning with a naïve crush and ending with an overwhelming sense of heartbreak and loss. Moreover, Fassbender’s performance achieves a level of energy and enthusiasm which trumps everything he puts forth in the moments he spends with Knightley’s Spielrein. In one small scene, for instance, after Jung and Freud excitedly converse about sexual topics for some time, the camera pans out to reveal that the two men are in the process of dining with the entire Freud family. This sequence serves only to emphasize Jung’s single-minded, subtly romantic obsession with Freud.

Still, like so many of the movie’s more memorable moments, the scene falls victim to tonal confusion — broad comedy and sharp seriousness collide with unintelligible results. Furthermore, the film simply does not spend enough time with Freud’s character, despite the fact that Mortensen gives the only stable performance in the entire piece. Because of its insistence on showcasing an unusually awful Keira Knightley and a shockingly boring Michael Fassbender, A Dangerous Method all but ignores its intriguing homoerotic undertones and Mortensen’s stronger supporting performance.