Nico di Angelo was walking along the shore of Long Island Sound. He had returned to Camp Half-Blood a few months ago, after disappearing for almost 1 and a half years. He was 16 now. He was a trained demigod. A lonely, trained demigod. People still feared him and treated badly since he was a son of Hades. But he was learning to accept it, even though he still hated that people acted the way they did around him. He was jerked out of his thoughts when he heard screams.
He ran for the entrance to Camp Half-Blood where people were gathered, trying to fight off a hellhound bigger that Mrs. O'Leary. He was wondering why they wouldn't just let the barrier around the camp keep out the beast. Then he spotted something in the hellhound's mouth. Held tightly, but not tight enough as to hurt or kill the person, was a teenage girl with pale skin and dark black hair. He unsheathed his blade and ran toward the giant hellhound. Nico jumped up and kicked the creature in the jaw as its head was lowered. The hellhound dropped the girl. It whipped around to face Nico. The hellhound growled and Nico started fighting it. The teenage girl began to stir. She sat up, holding her head, trying to deal with a massive headache. After many minutes of fighting, the hellhound knocked Nico into a tree, knocking him out. He was about to be turned into dog food, when suddenly the teenage girl stood up. She grabbed Nico's stygian iron sword and stabbed the hellhound in the ribs when it wasn't looking. It disentigrated, leaving nothing but a large pile of black dust. The girl collapsed, breathing heavily. Everyone was shocked, even Chiron, who had galloped to the entrance just in time to see it happen.
Later that day, Nico woke up in the infirmiry. "Dude, you feel ok?" Nico saw Will Solace, a son of Apollo standing over him. "Yeah... what happened?" Nico asked as he sat up, wincing at the pain. "The last thing I remember is being catapulted into a tree by giant hellhound." Will sat down in a chair and explained to Nico what happened after he passed out. Nico was shocked that the girl had killed the hellhound, despite, as far as he knew, not being trained and having previously been passed out on the ground. "So, who is she?" Nico asked. "I heard her name is Leyla Dalton. She's fifteen and she doesn't know who her godly parent is." Will answered. "I thought the gods were suppose to claim their children by the age of thirteen." Nico said, a bit confused. "They are,but for some reason, she hasn't been claimed. She's in the Big House talking with Chiron and Mr. D." Will said. "Ok, bye." Nico said, getting up. "See ya," Will replied as Nico left.
He headed to his cabin, walking past the Big House. As hed did, Leyla came walking out, Chiron and Dionysus behind her. they said something to her and she nodded. Leyla turned, heading towards the Hermes cabin, but changed direction when she saw Nico. She ran up to him and asked, "Hey, you're the guy that tried to save me from the giant hellhound, right? I'm Leyla. Your name is Nico, right?" Nico smiled a bit and nodded. Nico noticed that her eyes were each a different color. The left one was green but the right one was blue. Her black hair fell down her back and down the front of her shoulders down to her waist and was so dark, it was like staring into a void. Leyla caught him staring at her hair. "Whatcha lookin' at?" she asked him. "Uh, nothing. Anyways, thanks, you actually saved me. If you hadn't killed the hellhound with my sword, I would've been dog food." he answered. "If you hadn't stepped in I would've been dog food. So, thanks." Leyla replied. "Anyways, I gotta get to the Hermes cabin. It's where i'm gonna be crashin' 'til I find out who my godly parent is. Who's your godly parent?" Nico got nervous. "Um, it's Hades. Ya know, the God of the Dead and King of the Underworld." Leyla stared at him, then smiled. "That's amazing. Your father is a king! That's too cool." Leyla said, making Nico feel much better. "Well, gotta go. See ya later Nico." Leyla walked to the Hermes cabin and Nico walked to the Hades cabin.
About two months later, everyone was gathered around the campfire, singing camp songs and eating dinner. Everything was normal until the fire turned black and the fiery image of Hades appeared.
So, yeah, this takes place after the Heroes of Olympus series. I know the last book hasn't been released, but I'm writing this anyways based on current knowledge.