Sophie is a girl with six toes that David befriends. He discovers she has an extra toe when her foot gets caught and he helps her free it.
Looking back, David comments on the changes Sophie brought when coming into his life.
I was a normal little boy, growing up in a normal way, taking the ways of the world about me for granted. And I kept on like that until the day I met Sophie. (ch 1)
David describes her as a little shorter and younger than himself.
She wore reddish-brown dungarees with a yellow shirt. The cross stitched to the front of the dungarees was of a darker brown material. Her hair was tied on either side of her head with yellow ribbons. (ch 1)
David is surprised to see a child, or person, he has never seen before. In his close-knit community everybody knows everybody. It turns out that Sophie has 6 toes on one foot. This makes her a mutant and an aberration that is considered dangerous by the community.
David agrees to keep Sophie’s secret. She is a sweet little girl no different from himself. David has an aberration too—he is a telepath. His is easier to hide though.
David’s father beats him until he reveals Sophie’s existence, and at that point her family flees to the Fringe. David does not meet up with her again until much later, when she is no longer a sweet little girl. She is described as “degraded to a savage, with an arrow in her neck” (ch 17). Fortunately, David and Rosalind are rescued by the Sealand people.