A phone call that changes everything. A seemingly impossible challenge. Hours instead of months to prepare. When mezzo-soprano Deborah Humble received that unexpected call from the Sydney Symphony Orchestra, she faced a career-defining decision: step onto the stage of the Sydney Opera House that very evening to perform Gustav Mahler's Second Symphony—a piece she had never fully sung before—or walk away from the opportunity of a lifetime. What followed was a whirlwind day of frantic preparati...