By the end of their set at Madison Square Garden Friday night, the Strokes had tackled their biggest crowd-pleasers – from "Is This It" to "Repitilia" to "Juicebox" –when Julian Casablancas posed a question to fans. "Wouldn't it be great if Elvis Costello sang with us?" The arena roared, but Casablancas then dashed all hope. "April Fools! Just kidding – he's not doing it." Costello – who surprised Strokes fans earlier in the night by playing an opening set of "Pump it Up," "Radio Radio" and "(What's So Funny 'Bout) Peace, Love and Understanding" – had the last laugh, strapping on a Stratocaster Jazzmaster and joining the band on their ambitious new rocker "Taken for a Fool." Watch Rolling Stone's exclusive front-row video here.