Rarely has mailing a pair of 9x12 envelopes been treated more rapturously, but then Reprise doesn't convey just Phillip and Erik's youthful excitement. Writer-director Joachim Trier and co-writer Eskil Vogt take the young men's emotions seriously, but also observe them with some detachment, and a hint of mockery. This deft juggling of tone is one reason that the movie can be described as an action flick; the film's shifts in pitch are thrilling. So, too, are this existential romp's speedy flashbacks, narrated asides, impatient edits, and sprinting handheld camera. Reprise doesn't include car-chase scenes or the like, yet it's deliriously on the move. (Yes, Trier is a student of the French new wave, but he's also a former Norwegian skateboard champion.)

The scenario is commonplace, yet convincingly tangled. Of the two young writers, Phillip seems the more talented; his book is published first, and to acclaim. But he enters into an obsessive relationship with Kari (Viktoria Winge), attempts suicide, and is institutionalized. Erik stays steady, and eventually his book is also published — after much second-guessing of the title, Prosopopoeia. Along the way, we meet Phillip and Erik's friends, most of them somehow connected to a defunct punk band, Kommune, and also (just barely) Erik's neglected girlfriend. Than there's the publisher's assistant who's attracted by Erik's talent, but repelled by his circle's contempt for women. And, once in awhile, an appearance by Sten Egil Dahl, the reclusive author who inspired Philip and Erik — and who, they come to worry, isn't that great a writer, which may mean that they aren't all that hot, either.

If Reprise wonderfully captures the giddiness of youth, it also makes room for such doubts. Barely into their 20s, Erik and especially Philip worry that things they love have been lost and can never be retrieved. Tentatively reconciled with Kari, Philip takes her to Paris, where he compulsively reenacts the events of their previous trip there. (Guess which sojourn is more fun.) Twice, a narrator proposes absurdly far-reaching implications for the young men's lives and work. Yet the characters, and the movie, can also revel in a simple moment, such as the one where a party comes to life when someone puts on Le Tigre's "Deceptacon," and Norwegian reserve yields to American feminist synth-punk.

Joy Division, New Order, the Jam, and Norway's own Turbonegro are also heard in Reprise, but the film is not overstuffed with songs. Music is used sparingly, with new scenes often announced by a snippet of rock guitar. The style seems utterly contemporary, and while Trier has told interviewers that he was inspired by the '60s films of Alain Resnais and Jean-Luc Godard, Reprise is actually closer to Olivier Assayas's Late August, Early September (whose French literary-world characters are a bit older) and Roger Avary's underrated The Rules of Attraction (whose American college kids are a bit nastier). Endowed with a young's man's strut — Trier is 34 — but also imbued with melancholy and self-aware wit, Reprise is a rare example of a talky arthouse flick with the reflexes of a cheetah. The film moves beautifully, and it's a pleasure to be carried along by its rippling muscles. (2006, 103 min; opens Friday, May 23 at Landmark Bethesda Row)