The debut album from Swedish sisters Klara and Johanna Soderberg – aka First Aid Kit – is similar in tone to their 'Drunken Trees' EP, although it certainly sounds like the pair are continuing to mature musically and gain experience. A striking effort.

Over the past few years, the term 'YouTube stars' has become a tacky badge of honour for absurd videos like Keyboard Cat, or a fat kid swinging a lightsabre around his head. Yet teenage sisters Johanna and Klara Soderberg became stars of the site – and of the indie world – when their homemade cover of Fleet Foxes' 'Tiger Mountain Peasant Song' clocked up over a million views. Then signed to Rabid Records, the Stockholm label run by The Knife, the sisters released their debut EP 'Drunken Trees', and were subsequently picked up by the esteemed Wichita Recordings.

'The Big Black and the Blue' is First Aid Kit's debut longplayer for the label - but if you're thinking 'Teen sisters? Cutesy!', then think twice. This is dark-edged folk music, laced with a lyrical poignancy beyond the Soderbergs' years. The most striking thing about the First Aid Kit sound is not only their ability to harmonise in perfect pitch, but their talent at conveying emotion whilst doing so. 'Heavy Storm' and 'Winter is all Over You' are tales of sadness and loss, the latter delivering the evocative line "I saw your mother at the department store / She looked innocent, like a still-born" almost like it's a throwaway thought.

Musically, the pair make much of their simple tools, which are acoustic guitar and piano, occasionally supplemented by a cosy bassline or barely-there drum beat. It can all get a little intense at times, but the sombre mood is tempered by gentle upbeat rollicks, like 'Sailor Song', wistful airs that seem to float into the ether ('Will of the River'), and cheerfully contemplative numbers like standout track 'Josefin'.

It's an organic, impressive debut that's not perfect - but if First Aid Kit continue to make albums and progress, they could prove a highly valuable and influential asset to the folk scene this decade.