Nettie's first letter describes the immediate aftermath of her departure from Celie's and Mr. ____'s house, when Mr. ____ chased her down the road and tried to drag her into the woods and rape her. Nettie fought back, and Mr. ____ vowed that she would never again be able to communicate with Celie.
Mr. ____ was not content simply to let Nettie leave. Instead, he did everything he could to get her to become his mistress, and his desires for Nettie, here, perfectly echo Pa's desires for his own children.
Nettie fled into the town and stopped at the Reverend's house, where Celie had told her to go. Nettie recognized the young girl, the Reverend's daughter Olivia, as having Celie's eyes.
Nettie, like Celie, recognizes Olivia's parentage by the color and shape of her eyes, which resemble her mother's to an uncanny degree.