A young woman traveling through the Taiga, a shapeshifting animal who just happens to be her lover, a forest queen, and a crude and brutal rake— surprisingly, these characters are not out of a medieval fable. Instead, they are central elements of “The Hazards of Love,” the new concept album from indie favorites The Decemberists. The 17-song rock opera never stops plowing forward from the second it begins, with a mix of folk and in-your-face heavy metal that makes it one of the most inventive folk-rock albums in recent memory. Some songs do not succeed beyond their role as fragments of the melodramatic plot. But when the album is viewed as one cohesive folk-rock project, it acts as a bold statement of the band’s ambition.

While the Portland-based band’s previous album, “The Crane Wife,” showcased frontman Colin Meloy’s affinity for lyrical storytelling, “The Hazards of Love,” the band’s fifth studio recording, takes these inclinations to an entirely new level. An hour-long saga of compelling fury that demands to be listened to in its entirety, it follows the story of a young woman named Margaret as she falls in love with a shapeshifting faun named William whom she meets in the forest. In four acts, an evil queen and a villainous rake try to destroy the couple, but these hazards only succeed in ending their lives, not their love.

Beginning with a slow organ crescendo that leads into Meloy’s somber introduction in the first variation of a recurring “Hazards of Love” track, the first act progresses into bombastic power chords as Margaret enters the treacherous forest. The second act adds a reprise of “The Hazards of Love” through the eyes of her love William. The album reaches a peak with “The Wanting Comes in Waves/Repaid,” as William is confronted by the evil queen. Using the leitmotifs from the previous songs, the later half of the album describes the rake character and the abduction of Margaret until she and her lover find peace in death at the album’s conclusion.

Full of recurring motif variations and the numerous interludes, “The Hazards of Love” is best enjoyed as the sum of its parts, but its individual peaks are manifold. With its creative mix of styles, “Annan Water” is multifaceted enough to be able to fit eloquently into the overall theme and still function effectively as a self-contained statement. As the rhythmic bellows of the accordion and the acoustic guitar in the verse suddenly stop to make way for a chorus of singers accompanied by organ, the song gains a sense of completion and cohesion that some of the other tracks lack. It ends on an unexpected minor chord, setting the stage for the cut that follows.

Later, “The Hazards of Love 4 (The Drowned)” acts as a cathartic reflection on the album as a whole, seeming to emerge out of the rubble into a climactic and chaotic narrative finale, describing the peace that Margaret and her lover William find in a watery death. The grand instrumentation, complete with the accompaniment of lofty strings and a steel guitar solo, work to create this sense of closure. The pensive nature of the song as a mournful yet serene ending to the album is truly expressed as harmonies sung by the other characters are added on top of Meloy’s grief-stricken melody.

Several songs are not as versatile as the aforementioned cuts, contrivances seemingly designed only to set up a given mood, build the suspense, or introduce a new character. For instance, “A Bower Scene” consists of a single guitar riff that seems to be more like a long introduction to the next song to come. With its thumping power chords that build and regress, the track is designed only to give the story a treacherous feel and create tension as the narrative begins. When it eventually erupts into a bombastic heavy metal motif of the next cut or is repeated later on in the CD, the song’s necessity to the album as a whole becomes apparent as it effectively creates the suspense needed to drive the story forward.

The Decemberists deserve enormous credit for “The Hazards of Love.” They have created a unified work of musical art centered on a single story whose use of recurring themes, reliance on the striking contrast between balladry and heavy metal, and classic storytelling have allowed it to work as a whole. Several of the songs serve only to signify scene changes, build on character development, or establish a certain atmosphere, but the production in its entirety succeeds in expanding the limits of what modern folk-rock albums can be.