After "La Gioconda", Callas had no further offers, and when Serafin, looking for someone to sing Isolde, called on her, she told him that she already knew the score, even though she had looked at only the first act out of curiosity while at the conservatory. She sight-read the opera's second act for Serafin, who praised her for knowing the role so well, whereupon she admitted to having bluffed and having sight-read the music. Even more impressed, Serafin immediately cast her in the role. Serafin thereafter served as Callas's mentor and supporter.