The Stones entered the room after some five songs into the show. On 'Baby Please Don't Go' we see how the band slowly gets involved into the set. An impromptu blues jam ensued, and before the night was done, Mick Jagger, Keith Richards, Ron Wood, Ian Stewart, Lefty Dizz, Junior Wells, and Guy himself had all appeared on stage with Waters and his band.
Stu didn't play all night, but here's a snippet from a tune in which he accompanies Junior Wells. It's nice to watch the Stones being excited to meet their long-time idol, perhaps the greatest bluesman ever and, of course, one of the major influences which led to the formation of the band back in 1962.
Adapted from the following source: Steve Leggett, Checkerboard Lounge: Live Chicago, 1981, CD/DVD review, Allmusic, 2012.