The song's lyrics concern an apparently free-spirited woman, with Jagger singing,
"Who could hang a name on you?/When you change with every new day/Still I'm gonna miss you."
According to Keith Richards autobiography, Life, the song was written about his then girlfriend Linda Keith.
Linda had taken up with Jimi Hendrix, and had got involved with drugs.
She left Richards, and he tried to get her back.
He eventually went to her parents and told them she was going down a dark path.
Linda's father went to New York to collect her, and by order of court she was grounded.
Richards reports that Keith regarded this as a betrayal, and they did not speak again for many years.
According to Richards's autobiography, Keith survived, brought up a family, and now lives in New Orleans.