Since it would be unbearably bleak to show us nothing more than her decline, Eyre intercuts scenes of the old Iris (Judi Dench) and John (Jim Broadbent) with scenes of the young Iris (Kate Winslet) and John (Hugh Bonneville) during their courtship more than 40 years earlier. Of course, in some ways, this makes things even more depressing. We're constantly reminded of youth's inevitable slide from vigor and excitement to infirmity and death.
Eyre announces his intentions during the opening scenes: We first spy the young couple swimming naked, and in the underwater haze they suddenly age four decades. The combination of time frames is presented so evenly we can only tentatively suggest that the "young scenes" are flashbacks in John's memory rather than otherwise unmotivated directorial manipulations. Within each of the two time frames, events run more or less chronologically. We see John and Iris meet at an Oxford dance. They fall for each other at once, but the decision of long-term commitment is easier for him than her. He's a frumpy, ill-at-ease, stammering virgin; she's socially aggressive, wildly experienced, self-assured and put together like Kate Winslet.
While she quickly becomes the center of his life, he has to accept that she's not sleeping with him yet but is banging a moustachioed Dapper Dan. In a significant gesture, however, she does allow John to be the first one to read her as-yet-unpublished first novel, opening her mind to him more fully than she does to those with whom she shares her body.
Meanwhile, in the elder time scheme, we wince to see Iris, for the first time in her life, struggling with her manuscript; she can't remember a simple word. Rather quickly, her condition deteriorates to a level where neither she nor John can continue in denial. After she completely loses her train of thought in the middle of a TV interview, specialists confirm the worst: She will have to watch as her brain, her very sense of self, dies a little at a time. And, perhaps worse yet, John will have to watch it, as well.
Eyre--who, working from Bayley's two best-selling books of memoirs, co-wrote the film with Charles Wood, screenwriter of Help! and several other seminal Richard Lester films--takes some minor dramatic liberties regarding the time scheme. Most noticeably, Winslet comes across as a coltish grad student, though Murdoch was in fact in her mid-30s during her courtship with Bayley.
Dench is wholly extraordinary in a characterization that is frequently muted, literally and necessarily. The always wonderful Broadbent (Moulin Rouge and The Crying Game) is no less perfect, despite a large age difference.
The only real problem is Winslet, and the problem is more one of appearance than of her performance--she simply is not believable as a young Judi Dench. It's not a film-wrecking point, but it is the one little flaw in an otherwise perfectly tuned work.