It's seldom appropriate, or indeed fair, to compare a movie with the novel from which it derives. That becomes even more difficult when the source material is so extraordinary. Kazuo Ishiguro's 2005 novel 'Never Let Me Go' is a beautifully written, utterly compelling tome that lingers long in the memory of those who read it.

Set in a dystopian England of the 1950s, 'Never Let Me Go' is the story of three young friends growing up in a mysterious boarding school environment. The mystery soon becomes clear as we learn that these young people are here purely for the purpose of having their organs harvested by older members of society. This practice has resulted in life expectancy for society in general being extended beyond 100 years. But what are the personal and indeed moral implications for these living donors who, in true 'Logan's Run' fashion, are unlikely to see beyond 30?

These are questions that can be examined at leisure in the pages of a novel but it's director Mark Romanek's task to deliver an equally compelling screen drama, and in this he is only partially successful. The bleak story, as adapted by Alex Garland, unfolds through the eyes of one of the three designated clones, Carey Mulligan. As she and her two pals, now played by Andrew Garfield and Keira Knightley, reach their 20s, it's clear that the clock is ticking but their fate has been complicated by the strength of the emotional bonds that have developed between them.

'Never Let Me Go' examines major themes of life, love (it's rumoured that donors in love can defer their donation) and sacrifice, but the plot unfolds at such a glacial, ponderous pace that we need to care and empathise very deeply with the three main protagonists and herein lies the film's major flaw. Keira Knightley is not an actress noted for having empathy with an audience, while Andrew Garfield does his best with an underwritten role. The real strength of the film, therefore, lies with Carey Mulligan. This astonishing young actress has already made her mark in movies such as 'An Education' and the otherwise unmemorable 'Wall Street: Money Never Sleeps', and she is superb again here. For her performance (and Rachel Portman's score), 'Never Let Me Go' is just about worth a look.

Michael Doherty