In 1977, the Stones camped out in Toronto to play a rare club show and wait for the verdict in Richards' drug-bust trial. During the downtime, Jagger, with an assist from keyboardist Billy Preston, who toured with the band at the time, began working up a new song. "Billy had shown me the four-on-the-floor bass-drum part, and I would just play the guitar," Jagger says. Preston also wrote the song's slick bass line, which Wyman repurposed with "some changing and polishing," in his words. Richards sensed the origins of the song: "It was, 'Aah, Mick's been to the disco and has come out humming some other song.' It's a result of all the nights Mick spent at Studio 54." But thanks to the way the Stones attacked the groove (embellished by New York blues musician Sugar Blues' honking harmonica), this was disco as only they could do it. The ubiquitous single was the eighth and – at least for now – last Number One of the band's career. As Richards admitted, "As we got into it, it became quite an interesting beat."