"Zahra and Maryam have been best friends since childhood in Karachi, even though—or maybe because—they are unlike in nearly every way. Yet they never speak of the differences in their backgrounds or their values, not even after the fateful night when a moment of adolescent impulse upends their plans for the future. Three decades later, Zahra and Maryam have grown into powerful women who have each cut a distinctive path through London. But when...