A Dangerous Method. It takes place between pioneering psychoanalyst Carl Jung and his patient - and subsequently mistress - Sabine Spielrein, appropriately enough on a boat (Das Rheingold begins on the bank of the river of the opera's name, the Rhine).
The Wagner theme is developed as Jung and Spielrein (now acting as his assistant) make notes on the reactions of patients to the paying of a recorded excerpt of music from Die Walküre or The Valkyrie (a different excerpt from the famous 'ride' which is the prelude to the third act).
This is, in fact, the end of the explicit references to the composer. Yet Wagner's music both in original versions and in arrangements, sometimes for piano by Howard Shore continue to permeate the film, bleeding right across into the credits. Why is this?
Obviously in the first instance, Wagner's music has been referenced and needs to be played diegetically. The extract from Die Walküre has a particular pertinence given the sexual complications of the protagonists. Sabine references the darkness of incest and the guilt she feels at feeling aroused at her father's (non-sexual) physical sanctions. Not only is the opening of Die Walküre frenzied, dramatic, even intoxicating music. It also shows the reunion of a brother and sister who copulate and conceive. It is surely for this reason Jung chooses to expose his subjects to it. Indeed Sabine brings up the subject of incest explicitly. Here's the end of the first act as the brother and sister get it on:
More generally though, Wagner's music - which by dint of his manifesto (his own version of Dogme 95, if you like) Gesamtkunstwerk, is tied organically to the drama it represents - may be said to represent a welter of psychological insights, or at least clues, as to the thoughts and motivations of the characters in his dramas. Indeed, Wagner's operas are referred to as psychodramas. Clearly the use of the music is meant to not only support the film's drama but refer to the emotional currents hidden beneath the surfaces of the characters who either repress them or simply deny them as clinically symptomatic.
Consequently the extract that one hears as the men arrive in New York for the first time is strangely inappropriate. 'Mark my words,' says Jung, 'this is the future' as the closing music of Götterdämmerung sings out, music which in the opera accompanies the destruction of a palatial castle, ruined by fire and sinking into the Rhine. This doesn't seem totally right for a first glimpse of the freshly constructed high-rises of Manhattan. Better suited would be the equally lush music of the end of Jung's favourite Das Rheingold, that sees the opera's protagonists taking their place in this self same city shortly after its construction.
It is particularly noteworthy that the most persistent extract that Shore uses is of the Siegfried Idyll - which is not an opera at all. This piece was a short piece of music that he wrote as a birthday present to his wife, and received its first performance on the staircase outside their bedroom that morning. It is a love-letter, without a dramatic narrative and its plasticity must be its chief appeal to Shore. Here's a clip of the original.
(This link takes you to the piano version and the rest of the OST).