Heart Under, Just Mustard's second album and first for Partisan Records, is an album that asks you to forget what you know. At every turn, this remarkable record reconfigures and stretches the ideas and ambition of a rock band, and turns a year of lockdown and personal struggles into a breathtaking artistic statement. Across its 10 tracks, the album presents a coherent style and ethos – those scything guitars, Katie's magical vocals – but still incorporates a wide and untethered vision. There are brooding, atmospheric rock songs ("Still", "In Shade") and others that apply a lighter, dreamier touch ("Sore", "Mirrors"), all tied together with impeccable instrumentation and a united vision. On Wednesday, the band played with dreamier soundscapes and production techniques, and Heart Under serves as the next stage of this development, with every instrument brilliantly pushed to its limit and every boundary of the band stretched.