If you've read The Hitchhiker's Guide to the Galaxy (henceforward referred to as HHGTTG), the 26-year-old sci-fi-humor novel by Douglas Adams, then you know it starts with the end of the world, that it then follows the highly unlikely adventures of the miraculously saved British Earthman Arthur Dent, and that it's incredibly silly and utterly brilliant. Odds are, you read it young and it shaped your worldview. Possibly it became a part of you, a voice in your head sort of like a conscience but with a ridiculously absurd British sense of humor. And so you approach the movie version of the classic book with excitement, trepidation and a touch of paranoia (possibly because of the voices).

If you haven't read HHGTTG (henceforward HHG2TG), then I can tell you at least this. You know your friends? No, I mean the interesting ones-the creative, clever ones, the ones who like tinkering with things and figuring them out, the ones who always have such fascinating things to say? The ones who keep your computer running? I can tell you they've read it. And you should enjoy their company while you can, because eventually they're going to get tired of you.

Henceforward you will not be referred to at all.

Adaptation, both in nature and in movies, is hard-adapting HHG2TG (henceforward HHG2G) into a movie doubly so. The novel was itself adapted from Douglas Adams' radio play of the same name and as such has an extraordinarily strong voice. The book is, line by line, wonderfully written. Each sentence is solidly entertaining and fun to read, meant to make things happen inside our heads. How something is said-how it's written about-is often more important than the subject itself.

That's something movies aren't so good at. They're literal, visual and concrete, not verbal and abstract like radio.

The movie version of HHG2G (from now on, H2G2, for space) sidesteps this by focusing on the things a movie can do well. For instance, in the movie version, the famous last words of the dolphins to mankind ("So long, and thanks for all the fish!") are interpreted in an elaborate aquatic musical number that the dolphins perform just before they fly up into the sky.

Which is very, very, very funny.

Martin Freeman is a great Arthur Dent, Mos Def is a great Ford Prefect, Stephen Fry is a perfect voice of the Guide, and Sam Rockwell is wonderful as Zaphod Beeblebrox. With Alan Rickman weighing in as the voice of Marvin the chronically depressed android and Helen Mirren as the voice of the supercomputer Deep Thought, you couldn't ask for better casting.

When Slartibartfast gives Arthur a tour of Earth Mark II, we see with our own eyes a glorious world, from Ayer's Rock (still being painted) to the oceans (still being filled by a nice man with a hose) to the creation of the Himalayas ("Voila! Himalayas!" as Slartibartfast says). It's like a little visual Valentine to the Earth-Arthur's home and ours.

It's in these moments that the movie shows how deeply it understands Adams' book and his work. One of Adams' later books wasn't a work of fiction at all, but rather an ecological travelogue called "Last Chance to See," in which he evoked the plight of dying species and ecologies with warmth and poignancy.

H2G remains uncannily relevant today. The Guide itself-the fictional repository of all human knowledge, a funny, flawed little electronic book-is, for us, the Internet. And galactic president Zaphod Beeblebrox, while meant to be a generic satire on politicians, has too many George W. Bush moments for comfort, especially as played by Sam Rockwell.

Adams was a very funny writer, but the end of the world is no joke, nor are the absurd failings of human culture. These are the hard kernels of sincerity around which he built so much humor, and what made H2 not just a best-selling book, but a profoundly influential work of art.

Adams died in 2001 at the extraordinarily unfortunate age of 49. The movie is fine and stands on its own, but it works best as a tribute to the author and to what he gave us.

And while it might be highly improbable that a spaceship should ever turn, however briefly, into a giant picture of Douglas Adams' head-almost infinitely improbable, really-it does, blessedly, happen.