“Science Fiction,” Long Island rock band Brand New’s fifth and allegedly final album, starts off with some low-pitched strings and a framing device: a woman describing her dream to a therapist:

“The dream is that I’m in some sort of a…and I’m in a hotel I’m at…I’m like at a convention or something. And I feel sort of almost like there’s too much going on. There are all different kinds of meetings going on. Stuff on experimental psych and therapy, chemical aspects. All of it.

But, I’m… while I don’t mind having all this going on inside of me. It’s sort of… I think I’m going to be relieved when it’s over. When I can sort of settle back down.”

It is a strange sequence the first time through, immediately supplanting whatever expectations fans built up over the eight-year wait following the 2009 release of “Daisy” to mixed reception. It also describes “Science Fiction” perfectly: the unexpected result of years of soul searching. The album retains some of that unfamiliarity throughout its run, in all the right ways.

The worst thing that can be said about “Science Fiction” is that for a few moments here and there — particularly on “Can’t Get It Out” — Brand New actually sounds like Brand New. That is no real criticism, but it hints at this album being the final step of a stylistic progression they have headed toward since their earliest work. “Science Fiction” is as different from Brand New’s raw punk sound on “Deja Entendu” as Radiohead’s “Kid A” is from “OK Computer.”

This is not the Brand New you remember from your 2006 emo phase. “Science Fiction” is not the tortured beauty of a suffering teenager; it is magnificently maudlin, beautiful like a collapsing star.

“Science Fiction” is Brand New’s best work by a wide margin.

Lead singer Jesse Lacey and company have grown up a lot since we last heard them on “Daisy.” Besides just sounding an octave older, Lacey’s lyrics have evolved from the band’s earliest days. There are still the standard breakup ballads, but Lacey covers everything from aging to apocalypse, giving equal time to Christian dogma and nuclear holocaust.

It is still bleak songwriting, but the haunting melody of lyrics like “Let’s all go play Nagasaki/We can all get vaporized/Hold my hand, let’s turn to ash/I’ll see you on the other side” have an emotional impact far greater than older lines like “Today’s the day it gets tired/Then today’s the day we drop down,” from years past.

Thematically, Brand New has always taken a playful, tongue-in-cheek approach to its fame and impact, like the band is surprised it has any fans at all. That is still here to some extent, but it is far more subdued than ever.

This time around, Brand New uses songs like “Waste” to play with its former self, spending more time coming to terms with its past than teasing its supporters. Lacey sings lines like “It’s all in your head, your race is run/Don’t give up, my son, this is the last one,” offering comfort to the man he used to be. That weary maturity runs through “Science Fiction” like an ore vein.

“Science Fiction” showcases a band that has finally shed its insecurity. Whether they shed it by confidence or just the sheer erosion of age is anybody’s guess.

The album jumps genres quite a bit. There is some hardcore and alternative rock influence like always, but there are also hints of folk, blues and progressive rock. The sheer musicianship and musical density of the album is unprecedented in Brand New’s catalog; it is hard to imagine multi-layered songs like “137” and “451” finding a place in their earlier albums. There are scatterings of mandolin and cello and guitar riffs that could make John Mayer soil himself.

Brand New’s reliance on dynamics is nothing new, but it has perfected a certain subtlety with its craft on its latest effort. The musicians have mastered the art of the middle ranges; they can hit every volume from two through nine instead of just going from one to 10. “Science Fiction” makes its points with a whisper just as well as it makes it with a shout.

Lacey was lying when he said the band would take a new direction on “Science Fiction.” Really, they took about five, all of which work wonderfully.

At the end of “Science Fiction’s” hour-plus running time, Brand New manages to prove it picked the perfect title for its potential swan song. “Science Fiction” places the familiar within unfamiliar surroundings. It is strange yet relatable, foreign and all at once. This album is science fiction at its core, it is nothing if not a creative marvel.

If this is really the end for Long Island’s prodigal emo sons, it is a masterful final act. But if Brand New can make music this well, we can only hope this is just another beginning.