Don't be fooled by the immediacy of "Show Yourself." The latest single from metal masters Mastodon presents the band at its most streamlined – fast, direct, and with just enough of the edge turned down to avoid alienating anyone unfamiliar with the group's catalog. Mastodon members have described the cut as a gateway of sorts. That's accurate. But also consider it an introduction to another realm. Emperor of Sand, the new album from which it stems, continues the quartet's mission to conjure different universes, both in sound and in theme. Desert landscapes, loneliness, cancer mortality all make appearances on the work, full of multifaceted guitars and unyielding rhythms. Relentless, complex, and rife with metaphor, the album demands time – and respect. Its release also provides an opportunity to look back on five noteworthy heavy-metal concept albums.

Mastodon Leviathan
Mastodon's second album is its first with a cohesive theme, and the Atlanta-bred group aims big. Leviathan takes inspiration from Herman Mellville's Moby Dick. Sonically, the work reflects an intense, flesh-hungry-like ferocity. "Blood and Thunder" opens the set with fervent, tight, and forward-moving guitars from Brent Hinds and Bill Kelliher. Their instruments wildly circle around one another in the song's mid-section. Such concentrated force continues with "I Am Ahab," where drummer Brann Dailor darts left and right, equally full of muscle and ornamentation. But Mastodon yearns to tell a story, not pummel eardrums. Songs such as "Seabeast" and "Megalodon" play with tempos, illustrating that Leviathan is as full of emotion as it is obsession.

Iron Maiden Seventh Son of a Seventh Son
While only casually following a theme, Iron Maiden's seventh full-length represents the concept album at its loosest. The standout "Moonchild" creates a world of its own, with a patiently building arrangement that lets Dave Murray and Adrian Smith's guitars make an entrance – one that crawls, stomps, and then, knocks the house down. That says nothing of the otherworldly, vintage synth sounds draped over the arrangement. Throughout, Iron Maiden references its adventurous side, nodding to the experimentation of 70s prog pioneers as well as hard rock, be it the churchy "The Prophecy" or theatrically melancholic "The Evil That Men Do." Narratively, the band draws inspiration from Orson Scott Card's Seventh Son, a novel about a child born with magical powers. The science-fiction connection serves to heighten the mystery behind trippy songs such as "The Clairvoyant."

Opeth My Arms, Your Hearse
Ghost stories have long been enthralling, enchanting, and eerie – hinting at an afterlife while also managing to spook. On 1998's My Arms, Your Hearse, Opeth shows the ghost story can also be haunting and tragic. While the album – featuring relatively concise arrangements with weighty instrumentation – marks something of a departure for the Swedish group, it benefits by playing like one long song. Lyrics unfold in a novel-like manner, telling the story of a lonely, bitter specter doomed to watch the love of his life move on without him. Instrumental tracks hit like intermissions. Mikael Åkerfeldt's vocals range from low-down growls to heavily melodic, operatic wails (see "April Ethereal"). And as rough as the band can be, romantic ("When") and ornate ("Credence") moments abound.

Emperor Prometheus: The Discipline of Fire & Demise
Few moments in rock sound more unsettling than the opening seconds of Emperor's final album. The Norwegian metal pioneers, whose members boast a convoluted, controversial, and darkly violent history, launch the work with a gust of wind, whispers, and ghastly strings. It only gets weirder and more complex from there. Taking its name from – and chronicling the journey of – a Greek god, Prometheus: The Discipline of Fire & Demise survives as the sort of demented work that seems hard to ignore. "Depraved" is just that, with odd, manic sounds that come across like hospital machinery burrowing beneath the guitars. "The Tongue of Fire" arrives as a clash of tones, with Ihsahn's fiery howls and Samoth's angular guitar work resonating amidst brightly atmospheric synths. All distorted and grimy one moment, the song becomes clear and focused the next, capturing the variances of a symphony.

King Diamond Abigail
Prepare to be creeped out. King Diamond's supernatural horror story, set in the 1880s, has a bit of everything: castles, mysterious horsemen, murder, possession, betrayal, and a demonic, unborn child. It's also an engrossing character study, with the singer donning and discarding voices at will. Stay home, put Abigail on, and turn off the lights, and you basically have a makeshift night at the theater. Or ignore the story and marvel at the diverse sonics – whether the hurried call-and-response choir of "A Mansion in Darkness," spiraling leads of "The Family Ghost," or front-and-center rhythms and lock-step riffs of "Shrine." Diamond's marvelous soprano soars above each of the arrangements, and oddities lurk around every corner, such as the twisted, haunted-house organs that arrive in the final moments of the title track.

Photo credit: Jimmy Hubbard