Cassie's unreleased classic

In 2008, the idea that one's musical taste is tied to such archaic factors as release dates or actual product seems almost quaint. After all, this is a year in which my favourite track doesn't officially exist. Cassie's Turn the Lights Off is a spellbinding piece of minimal, late-night R&B. Dark and seductive, its hypnotic high end and Cassie's ice-queen delivery perfectly capture a physical state of subsumption. "I'm not afraid, afraid of the dark," she intones, preparing for a plunge into the unknown.

It isn't available to buy anywhere and YouTube posts tend to get blocked (though anyone with the barest minimum of internet savvy will be able to track down others within a couple of mouse clicks). It was one of the first tracks to leak from Cassie's much-delayed second album, tentatively titled Connecticut Fever (originally scheduled for September 2007, its release date is receding ever further into the black hole of "early 2009"). It wasn't the last: throughout 2008, enough songs from Cassie's studio sessions found their way online to make up the whole album. Each is magnificent: had Connecticut Fever existed, it would be an easy contender for album of the year.

Is It You and Official Girl were Cassie's only official 2008 releases. The former is a delightful bubblegum pop song made touchingly human by the hint of tentativeness in Cassie's performance: the slight gasp she gives after the line "I'm looking for someone to share my pain," for instance, as if mindful of the risk she's taking in revealing too much of herself. On Official Girl, meanwhile, producer Danjahandz swathes her in candy-floss production as Cassie demands clarity in a relationship: she cajoles, threatens, pleads, swears she can measure up. The song climaxes with the frankly brilliant line, "I ain't making ultimatums – I'mma tell you like this verbatim!"

As will be apparent, Cassie is a technically limited vocalist and, like fellow thin-voiced divas such as Janet Jackson and Ciara, she has been criticised for these shortcomings. Thirsty, though, is a great example of how Cassie turns her weaknesses into strengths. Taking her signature fragility to an extreme, she essays a performance which is even more dream-like than usual. The pay-off is a brilliantly paced middle eight on which, having tantalised her suitor with the promise of being "fully submersed", Cassie turns and flicks him away: "I think about it, I doubt it, should make you live without it and keep you dying of thirst – I'm just playing with you!" By contrast, the lush, opulent My House finds her a remote, beckoning figure, floating passively through the corridors of an empty castle, awaiting rescue.

The freestyle influence on Cassie's sound is important: it's apt that she takes so many of her cues from this 80s dance subculture. The echoing, stabbing synths on Activate and its invitation to "bring your senses to me tonight" are the most explicit manifestation of this, but In Love With the DJ is an extraordinarily accurate commentary on clubbing culture. Cassie knows the desire to cede control to the dance floor; her double-tracked vocals on the chorus – one Cassie blank and robotic, one Cassie reaching for ever higher levels of bliss – are pure genius.

The starburst synths of In Love With U deserve attention, too, but it is 2 the Morning that stands as Cassie's richest, fullest and oddest track yet. Over lurching beats and cushions of cut-up chorales, she murmurs sensually while being drunkenly dive-bombed with bass. It's both disorientating and incredibly tactile, and as oddly captivating as the rest of her material.