Bloody hell, this is a depressing film. Watson, Mrs Hudson and Moriarty are all long dead and the glory days of Sherlock Holmes are long behind him. Surprisingly, when you consider his history of poor nutrition and his period of substance abuse, a 93-year-old Holmes is the last of the old guard. This is an adaptation of Mitch Cullin’s excellent book A Slight Trick of the Mind, which tells a story not often told: what happens when you go beyond the beginning of Holmes’ cosy cottage retirement into the last few years of his life?

Turns out there’s not much difference. He still keeps bees, is still his same old isolated self and is still (in a way) solving cases. But now there is one significant difference, one that drives the whole story: Holmes is, to put it in scientific terms, losing his marbles. We never expected a Sherlock Holmes story to be fully comparable with the Daniel Keys book Flowers for Algernon, but here we are. Here, as in that volume, the great tragedy is the loss of a remarkable intellect, although at least Holmes has had his full lifetime to take advantage of it. But it’s still heartbreaking.

Part of this comes about through Sir Ian McKellen’s superb performance. In both time periods in which the film takes place (1947 and about 30 years before, at the time of his emotional upheaval), he plays the part with quiet dignity and the kind of wry humour that the literary character was so known for. His refusal to play the part with overacted sobbing fits really helps the film, as the nearly two-hour running time gives you time to understand just how broken he is without having to resort to cheap tricks.

The running time also gives us time to appreciate the beautiful cinematography on show here. In the tradition of the best period pieces, like O Brother, Where Art Thou or Indiana Jones, it feels like we could step through the screen and end up in another time.

It’s difficult to think of any issues with the film. Purists might take issue with the revised ending of the book, but they’re wrong to do so; the new one works as a more filmic ending. As so much of the final part of the novel is dependent on the detective’s inner monologue, it’s difficult to convey that into cinema that works. Not impossible. But difficult.

There we have it: not only is it a fantastic Sherlock Holmes story, it’s a fantastic film; one that will stick with you long after the lights have come up. Easily one of the best film we’ve seen all year.

MR HOLMES / CERT: PG / DIRECTOR: BILL CONDON / SCREENPLAY: JEFFREY HATCHER / STARRING: IAN MCKELLEN, LAURA LINNEY, HIROYUKI SANADA, MILO PARKER / RELEASE DATE: OCTOBER 26TH