The hairs belonged to Lucy's mother. Dr. Manette had them wrapped and wore them around his neck. The hairs had been found on his sleeve when he was arrested, and he had kept them to remind him of the woman he loved.
Releasing his arm, she laid her hand upon his shoulder. After looking doubtfully at it, two or three times, as if to be sure that it was really there, he laid down his work, put his hand to his neck, and took off a blackened string with a scrap of folded rag attached to it. He opened this, carefully, on his knee, and it contained a very little quantity of hair: not more than one or two long golden hairs, which he had, in some old day, wound off upon his finger.
He took her hair into his hand again, and looked closely at it. "It is the same. How can it be! When was it! How was it!"
As the concentrated expression returned to his forehead, he seemed to become conscious that it was in hers too. He turned her full to the light, and looked at her.
"She had laid her head upon my shoulder, that night when I was summoned out—she had a fear of my going, though I had none—and when I was brought to the North Tower they found these upon my sleeve. 'You will leave me them? They can never help me to escape in the body, though they may in the spirit.' Those were the words I said. I remember them very well."