I often call the Mercury-Pluto hard aspect combination the "Finding Your Voice" archetype, and I cannot think of a more vivid example than this film. Colin Firth plays the king, and throughout the film we see him engaged in what appears to be a life and death struggle with a crippling stammer. His being born into the royal family is a particularly cruel fate, as duty often demands that he give public speeches, and as it becomes clear that he must take on the responsibility of becoming King, his burden becomes exponentially more difficult. He engages the services of a speech therapist, played wonderfully by Geoffrey Rush, and the drama of the film plays out as Rush's character struggles to assist the king in overcoming his stammer.
Mercury, of course, is the planet that rules speech, communication, and the voice. And Pluto is the archetype of struggle, intensity, life and death drama, and the dialectic between repression and the cathartic release of the repressed. Pluto, at the problematic end of the spectrum, can relate to things that are totally repressed, controlled, and -in a sense- held captive in the underworld. And this is what we see in the film with regard to the King's ability to communicate clearly (Mercury).
The film also makes clear that the root causes of the King's stammer stem from painful wounds suffered in childhood (many of which having to do with parental power and control manipulations), and this clearly relates to the Pluto archetype as well. Pluto can be seen as our own personal underworld of repressed pain (Freud's Id), and with Mercury it fits that in this case the King's personal underworld erupted symptomatically in the form of his strong stammer. It really fits that King George VI has the Mercury-Pluto alignment on his Sun as we see that so much of his pain stems from painful wounds with major male figures (his brother and his father). Sun-Pluto can be the "Powerful Father" archetype, and it also really fits his own struggle to come into his power as a leader.
Mercury-Pluto at the positive end of the spectrum is the "Powerful Communicator" archetype, and you often see it in great public speakers (like Winston Churchill who has the opposition). Pluto at its best brings empowerment and a capacity to tap into a force of nature, and with Mercury it can empower the voice. And thus we see King George's journey from the shadow side of the archetype at the beginning of the film to the most positive form of the archetype at the end. It is a great example of how a hard aspect alignment can be very difficult, but can ultimately be worked with until a much more positive form of the archetype is manifested.
It is striking to me that during the entire theatrical run of this film (the film opened on December 10th) we have had a collective Mercury-Pluto conjunction in the sky. This is quite a rare thing for a Mercury-Pluto conjunction like this to last so long, and only happens when a Mercury retrograde cycle happens to overlap with a Mercury-Pluto conjunction, as has happened here. Also striking is that Colin Firth has the Mercury-Pluto archetype strong in his natal chart as well. In his case it is a mid-point configuration: his Sun is at the Mercury-Pluto midpoint. His is a particularly powerful midpoint configuration as it is also basically a broad triple conjunction with Mercury and Pluto 10-11 degrees on either side of his natal Sun.
King George birth data: AA data according to Rodden Astrodatabank.
Colin Firth birth data: no birth time, just date of birth from Wikipedia. Noon Chart.