I'm not an expert in the history of codebreaking, computers, and the Enigma machine. I can tell you that the role of the Poles in real events is sadly underplayed, not just here but in essentially all movies about Enigma. The Poles acquired the first Enigma machine--the original three-reel one, mind, but still. The Poles contributed quite a bit toward breaking the code, too. It's not as egregious as a certain American movie implying that the work was all done by Americans, but still.
Thomas Jericho (Dougray Scott) has worked himself into illness in breaking Enigma code. (Even with the machine, there was still quite a lot of work involved in getting the day's codes--and the Engima settings were changed every day.) He was sent off to Cambridge to recover; now that he has, he's back. Claire (Saffron Burrows), the girl of his affections, disappears, and Jericho adds the search for Claire into his obsessive work. To both ends, he enlists the help of Hester Wallace (Kate Winslet), and he works very hard at driving her past the point of madness as well--or at least getting her arrested for treason.
Very few movies bother making mathematics and such interesting. However, this one shows a group of nerds being fascinating, and they are deeply devoted to winning the war for Britain. They follow the great convoy battle with fear and fascination. They want to get enough transmissions to break the day's code, but at the same time, they're afraid that, if they do, lives will be lost. It's a horrible bind to be in, but there they are. It's their job to break the code, and maybe breaking the code will save more lives than will be lost in the convoy battle. It's the same bind people were in all over the war.
The spy story, frankly, feels silly. It feels stuck on because the mathematicians really aren't that interesting. I think they are, of course, but my opinion doesn't seem to matter. To the average person, I suppose, the drama of codebreaking, even with a love story tacked on--and there are many other ways to tack on a love story--is rather dull. This regardless of the fact that the fate of Europe hung in the balance. It's as I was saying the other day--the reason Apollo 13 got made into a movie and Apollo 11 didn't is that most of the story of Apollo 11 is technical, and the technical stuff is boring. It's the human drama that matters. However, the spy story is just complicated and unbelievable.
I understand that it's based on a novel, and the odds are almost certain that the novel is better. However, we do get a Tom Stoppard screenplay, here, and there ain't no stoppin' that Tom Stoppard.