Hazel choked back a sob. “Nico… Oh, gods. The seeds.”
“You know what they are?” Annabeth asked.
Hazel nodded. “He showed them to me once. They’re from our stepmother’s garden.”
“Your step… oh,” Percy said. “You mean Persephone.”
Percy had met the wife of Hades once. She hadn’t been exactly warm and sunny. He had also been to her Underworld garden—a creepy place full of crystal trees and flowers that bloomed bloodred and ghost white.
“The seeds are a last-resort food,” Hazel said. Percy could tell she was nervous, because all the silverware on the table was starting to move toward her. “Only children of Hades can eat them. Nico always kept some in case he got stuck somewhere. But if he’s really imprisoned—”

The Mark of Athena, Chapter XIV