In the beginning of the episode, while Percy and Annabeth are talking, she takes hold of her camp necklace, in particular a ring that is on the necklace. While it has not been mentioned in the show, this was a present from her father that he sent to her in an attempt to reconcile their differences. The ring was a reminder to her father of his days in college and of Annabeth's mother Athena.
The title of this episode "I PLUNGE TO MY DEATH" comes from Chapter 13 of "Percy Jackson & the Olympians: The Lightning Thief" book.
In mythology, the hero Bellerophon (himself a son of Poseidon and, therefore, half-brother to Percy) threw a spear with a lead point down the Chimera's throat. The Chimera's fire melted the lead which choked the monster to death.
The episode covers the events of chapter 13 and 14 of the Lightning Thief book.