Faithfull brushes the fringe of dusty blonde-going-on-grey hair from her eyes, “but in an identity crisis what you do is say, ‘I can’t remember who I am; I’d better go and look in the mirror.

Faithfull, with Jagger, backstage at the Royal Court Theater in 1967 after her first-night performance as Irina in a production of Anton Chekhov’s “Three Sisters.” ...