Alzheimer’s disease is not fun. If you’ve ever been in contact with someone suffering from it, this is an understatement. It’s an unfortunate situation where a part of the brain gets disconnected, and you get lost even in the most familiar places. Iris Murdoch, English author and philosopher, became afflicted with it in her later years. Her husband wrote about his experiences with the situation, and Iris is based on his writings.

But the film is not about Murdoch, although there is much talk about her writing and influence on modern society in England. The film, rather, is about the disease and a relationship between two people who are faced with it.

And in that regard, the film is a triumph.

Nominated for three acting Oscars, Iris boasts powerhouse performances from Judi Dench, Kate Winslet and Jim Broadbent. Dench and Winslet play old and young Iris, respectively. Broadbent and Hugh Bonneville take on John Bayley, the man Iris married. The film constantly and effectively flashes back to Iris and John in their younger years each time she (Dench) stumbles across something that jogs her memory.

Dench tackles Iris at the beginning of her decline and gives us subtle moments of uncertainty and all-too-temporary memory losses.

Dench uses her eyes to tell her story – the mix of blank looks with concentrated stares she employs tell us everything we need to know. Her impeccable timing when required to utter a repetitive line is as frustrating as it is heartbreaking. Her bursts of violent reactions suggest how distressing it must be as her character’s once-strong hold on the English language dwindles into incoherent muttering.

While Dench’s Iris epitomizes fragility, Winslet’s newfound maturity further illustrates just how far Iris falls later in her life. Young Iris sits in a pub with an assumed lesbian while waiting for John. In this scene we see all the secrets she’s hiding and all the intelligence she possesses with nothing more than a glance.

Winslet plays Iris as a fun-loving, care-to-the-wind promiscuous woman who knows her place in life. As the insecure John courts her, she sternly makes it clear he will have to accept her for who she is. Winslet also shows no fear in a role that requires full nudity in most of her character’s scenes as much of John and Iris’ relationship grows from skinny dipping escapades. This is a far cry from her previously nominated works in Titanic and Heavenly Creatures.

As for the two John Bayleys, Bonneville looks like Broadbent if he had been cloned 30-some years ago. Not just their similar personas and mannerisms, but their chubby and wide-eyed faces are a dead match and make for perhaps the most inspired dual casting in some time.

It isn’t clear which actor takes the cue from the other, but it proves ultimately inconsequential when their performances are viewed separately. Both portray awkward posture, signifying their perpetual insecurity. As they stumble over their words, whether about Iris or directed toward her, Bonneville and Broadbent truly convey the essence of a man who is in love with a woman clearly more powerful than he.

The film is flawed, though, because it leaves the viewer asking too many questions about Murdoch’s life between her youth and old age. Granted, Iris is about a woman with Alzheimer’s, and that story translates beyond this one character. However, too much time is focused on who she is and her seeming importance. The only defense is that this is a film showing that the disease can affect even the strongest of minds – but that message gets lost when the viewer is asked to identify with a character whom American audiences might not be familiar with.

All in all, Alzheimer’s disease is not fun. That understatement is skillfully evident, courtesy of knockout performances from some of Britain’s foremost actors. B

• Only playing at Channelside Cinemas