Goth metal legends Therion are set to release their new album Beloved Antichrist next month. But this isn’t any ordinary album – this is a rock opera spread across three full-length CDs. Beloved Antichrist, inspired by Vladimir Solovyov ‘s A Short Tale Of The Antichrist, is a sweeping and thrilling performance using male and female vocals across 30 different characters, melding the classic arrangement of the traditional opera with the dark and fruitful metal output of Therion.

A colossal undertaking and a life-long ambition, Therion’s guitarist, founder and the album’s mastermind Christofer Johnsson, is putting the finishing touches on the band’s most ambitious release to date. “If I said Jesus Christ Superstar,” Johnsson begins, “You wouldn’t say ‘Oh, that’s a great album’ - it’s a rock musical written for the stage. [Calling this] “rock opera” is maybe misleading while this, the correct terminology for this would be a rock metal musical with opera vocals.

“In 2003 I started writing a classical opera, but I didn’t complete it – my way of thinking musically is a bit too damaged by rock music. I came to the idea of making an opera you can perform as a story, contemplating good music that goes with it.”

Listening to Beloved Antichrist, it’s clear that this is a conceptual story that explore many opposing themes and ideas. It’s heavy, gloomy passages, it’s euphoric choral runs, you might think it was set up to be something of a marriage between heaven and hell, the opera and Therion. “The thing is, when you write music it has to reflect these things,” says Johnsson. “There’s no planning or big visions when you write a normal album but here you have a story, big themes. You need to make a schedule, write music for each scene, music that reflects action on stage and emotions. Dialogue between different characters needs certain types of voice and you need to write for that.

“Reflect the lyrics, reflect what they’re singing about. When you have this length of music you can’t just write everything in E or A minor like most metal bands do. You need to value the keys, analyse the progression.”

The 30-year evolution of Therion from death metal pioneers into invaders of the world of classical music, styling their work as symphonic metal, marks only beginning of the band’s great ambition. Open-minded and their creativity boundless, Therion have far more material than can be heard on the album – and one day, Johnnson hopes to invade theatres and concert halls the world over with a full-scale production. “It has to be performed live on the stage,” he says, “I see a full-scale production with sets and props and lights and all kinds of glorious things. One day.”