Now why was I slightly disappointed by Source Code? I found it vaguely unsatisfying, and everyone else has seemed to rave about it. It is pacey, elegant and smart. Its four main characters are well-cast and do their jobs extremely well, but still I was left with the niggling feeling that, though I had suspended an awful lot of disbelief, once I had suspended it, the story still tried to stretch its alternate truth beyond the limits of my re-aligned credibility. Jake Gyllenhall, handsome, winsome and immensely likeable is repeatedly thrown back into the last eight minutes of a train journey, about to come to a horrible conclusion caused by a una-bomber figure whom he has to try to identify. He is being sent back by a strange organisation run by Jeffrey Wright, and his liaison within the organisation is the excellent Vera Farmiga – their relationship, by far the most interesting in the film, is reminiscent of that of David Niven and Kim Hunter in A Matter of Life and Death, but without the romantic entanglement (the other films that I kept being reminded of  were, of course, Groundhog Day, and also an obscure British film of the 1940s, The Interrupted Journey). Within the confines of these eight-minute interludes, whilst desparately searching for the bomber, poor, brave, doomed Jake also manages to find time to fall in love with his travelling companion, Michelle Monaghan, and herein lies the problem – he, understandibly, doesn’t want her to die. But in the supposedly real world, she already has died – he is only being sent back to try to identify the bomber to stop future atrocities, not to tamper with one that has, to all intents and puroposes, already happened. The niggling unsatisfactoriness comes from the way the film deals with this seemingly insurmountable problem of time-travel (though we are told that this is not really what is happening ) altering the past.

Perhaps I am being too fussy. Go to the film. Enjoy it for all its extremely good things – it is sensationally shot and looks wonderful; it is exciting, sometimes funny and, occasionally, moving. Ignore the niggles and you will have an entertaining evening in the cinema.