A reader at Internet Movie Database observes that “Enigma” is “history without histrionics.” This is meant as a compliment, and I agree the film’s low-key attitude is admirable — in theory. In practice, perhaps some histrionics might have been preferable to what the film gives us, which is passionless, murky drama from behind the scenes of World War II.

This is a story based on real events, dealing with the British math nerds who intercepted German messages and decoded them with the help of a machine called “Enigma” that they stole from the Nazis. I believe there are people who understand how the encryption took place, and how the machine decrypted the messages, but I am not among those people. Screenwriter Tom Stoppard might know — he is very smart, after all — but all that the scenes of coding and decoding did for me was make me frustrated that I couldn’t grasp what was being taught to me.

It is not essential to understand that part of the story, though, because there are people involved, too. First there is genius mathematician Tom Jericho (Dougray Scott), who has been on medical leave after a nervous breakdown he suffered when colleague Claire (Saffron Burrows) broke off their relationship. He has been called back into duty because the Germans have just gotten more clever with their codes, and he’s the only one nerdy enough to crack them.

Claire has now disappeared altogether, though, and Tom is concerned. He is even more concerned when he discovers un-decoded German messages stashed in her bedroom. With the help of Claire’s bookish roommate Hester (Kate Winslet), Tom sets out to find out why Claire had these, and where she is now, and would she please consider going out with him again?

So maybe Claire was a mole, and maybe Tom and Hester had better find her before dashing inspector Wigram (Jeremy Northam does). Meanwhile, though, the Germans are about to attack a fleet of merchant ships in the North Pacific, which might be a more pressing concern.

The movie is directed by Michael Apted (“The World Is not Enough,” “Enough”), and it should be noted that Stoppard’s screenplay was based on Robert Harris’ popular novel. I have not read the book, but I can’t imagine it is as difficult to sift through as the movie is. The film seems so intent on NOT being a typical, Hollywood-ized espionage thriller that it forgets why those films are often successful: because they are exciting.

Here, though, there are hushed whispers about this and that, and some frantic racing around, but it’s never very clear what’s at stake. And when everything is finally unraveled, and the true bad guys are revealed, I can’t confess being a) surprised or b) interested. “Enigma” is a good name for a movie this delibrately obtuse and unapproachable. It is a waste of good performances and an interesting historical event.

C (; R, some harsh profanity, one scene of sexuality,.)