(Self-released, digital) Released in late August, Mystery at Sound Lake is Burlington psych-pop outfit the Burning Sun's first new material in more than three years. Its dozen tracks mark the culmination of the group's spiritual quest to assert its identity — and cement its legacy — as one of the area's boldest musical endeavors. On its second and final studio album, the band effuses and erupts, meeting a pledge to lead listeners on a stunning voyage. Along the way, the Burning Sun enthrall with a sound they've labeled "mystical adventure rock." Though the recording completes the band's mission together, it should captivate long after the members go their separate ways. The Burning Sun originally formed as a trio with Katy Hellman, Bo Malcolm and Steven LeBel. Hellman has been the lead songwriter and vocalist; she and Malcolm have shared guitar and bass duties while LeBel has been on the drums. The new record also features Addie Herbert, whose vocals and guitar contribute to this dense and striking follow-up to the band's contemplative 2021 debut, Marrow. Mystery flows with illusory resonance from the start with the gleaming title number. The thoughtful opening arrangement gives equal space and volume to the mix of instruments — including piano and harp, too — and its various sections are revealed in startling succession. Sudden pauses and explosive restarts help the group lift off, setting a deliberate tone for the album. Mystery lays bare some of the Burning Sun's obvious influences, including the Cranberries and their lead vocalist and lyricist, the late Dolores O'Riordan. The band explores the path forged decades ago by classic psychedelic acts Jefferson Airplane and the Mamas & the Papas and rejuvenated by contemporaries such as Florence & the Machine. Much like those groups, the Burning Sun wield vocals as their centerpiece. Mystery is a demonstration of Hellman's prowess. She sings from a place of solitude and darkness as the ambitious "Bottom of Wells" billows and ultimately thunders under her signal. Her voice climbs to incredible heights over the ceremonial chanting of her bandmates and daunting crash and vibration. Hellman veers close to a yodel to start the curious "Jinx," a showcase of her ability to alter the mood and apply suspense with the slightest tonal adjustment. On the booming worship "Prince Matthew," she is a driving force. Mystery was recorded in Burlington by the esteemed Benny Yurco and mixed in…