The stakes are high as the remaining "American Idol" finalists sing their hearts out in hopes of winning America's vote and advancing to the next phase of the competition. In this episode, each contestant will perform one inspirationally powerful "showstopper" song, with the help of former Idol hopeful and now GRAMMY Award-winning artist, Lauren Daigle, who serves as celebrity guest mentor. Each finalist will also take on a song performed at the famed Woodstock music festival in 1969, which remains one of the most historic moments in popular music history. Sunday night's show will be the final opportunity for the judges to use their coveted save on one contestant this season. Last season's second runner-up and powerhouse vocalist, Gabby Barrett, returns to the Idol stage to perform her latest song.