Grushenka is the woman whom old Fyodor and his son Mitya compete for, a twenty-two-year-old with white skin and grey-blue eyes, who lives in a rented pavilion belonging to the widow Morozova, kept by the old merchant Samsonov. The onion is the fable she tells Alyosha on the night after the death of Elder Zosima.
Grushenka was seduced and abandoned by an officer five years ago, was taken in by an old merchant, Samsonov, and learned to bargain. She torments the two Karamazovs with her game. On the night after Zosima's death, Rakitin takes Alyosha to her house to see the fall of the righteous man, and she plans to devour him; but when she learns of the death, she jumps off his lap and crosses herself. Alyosha tells her he has found a sister.
She then tells what she heard from the cook Matryona: a wicked woman dies with no virtue except an onion she gave to a beggar; the angel holds the onion out over the lake of fire, the other sinners cling to it, the woman kicks them away, and the onion snaps. She tells this against herself, and confesses that she wanted to destroy Alyosha. He says he once gave her an onion too, the smallest of all.
The word returns in Alyosha's dream, when Zosima says that he too gave an onion and for that reason is at the feast. It is the novel's measure of goodness: a minimal gesture, without calculation, that proves no virtue and yet weighs. Grushenka reappears as the one who vouches for Mitya's word in the investigation, and as the woman from whom Katerina Ivanovna asks forgiveness.