“It is not predictable, my mind” sings Amirtha Kidambi on the opening track on Mary Halvorson's seventh album as leader. The guitarist's words, part of a set of lyrics she prepared for the album, resonates with her reputation as one of the most idiosyncratically leftfield improviser-composers of her generation. Though she's recorded songs previously in duo with cellist Jessica Pavone and is the unlikely vocalist for People, an alt-rock band led by lunatic drummer Kevin Shea of Mostly Other People Do the Killing, Code Girl (a 2CD set) is her first song-based album as leader. Kidambi, who is trained in the South Indian Carnatic tradition and has influences that range from underground rock through to European art-song, is teamed with Halvorson's current collective trio Thumbscrew (drummer Tomas Fujiwara and bassist Michael Formanek) and the Blue Note-recording trumpeter Ambrose Akinmusire, whose unique brand of blustery, vocalised introspection fuses perfectly with the dark intensity of Halvorson's songwriting. Kidambi's vocal interpretation is penetrating, persuasively so, yet feels a little dry and jarring in places for those not entirely familiar with the more avant-garde areas of vocal music. However, there are as well occasional echoes of alt-rock female singer-songwriters such as PJ Harvey and Fiona Apple, an influence on Halvorson's work. Her guitar, meanwhile, isn't compromised by the new vocal format: it's still the sound of surprise.