The Heroes of Olympus The Lost Hero

This is 1st book by Rick Riordan following the Percy Jackson series after the great war with the Titian's. They are defeated but there is a new enemy on the rise who wants wrath upon the Gods and demigods for destroying her Titian's. Percy Jackson is missing. Jason, Piper, and Leo are the new heroes in this book. Jason wakes up with no memory, with friends, and people he doesn't recognize. He is the son of Zeus. Piper is the daughter of Aphrodite and Leo is the son of Hephaestus the God of fire and blacksmiths. They attend the Wilderness School for troubled kids. While on a field trip their class is attacked and their teacher is killed.  Piper's dad was kidnapped by the giants. The 3 of them are sent on a mission to rescue Hera who was kidnapped when Zeus shut down Olympus.
      Leo discovers a secret cave at camp half blood and he finds a dragon made out of metal. He fixes it up and uses on the mission. He can make things randomly appear, control metal, make stuff, and has a rare fire power. Leo is traumatized by thinking that he killed his mother when he was young but it really wasn't his fault. Hera has tormented Leo since he was a baby and she still does. He isn't very excited about freeing her. Even though Jason has amnesia he knows he doesn't belong in camp half blood. He later discovers that his sister is Talia. Piper has the gift of charm speak. Her dad is a famous actor. They are part of a prophesy of 7 demigods that are supposed to try to save Olympus from Gaea and the Giants. On the mission they are attacked by cyclopes, encounter a King Midas, and meet Medea. When they encounter Medea they discover that their teacher Coach Hedge is still alive.
      They are all supposed to be dead. The Underworld is starting to bring back people and monsters that should be dead and monsters don't stay dead. They can materialize instantly. They also visit Aneomi the wind God to help find the Wolf house where the Goddess Hera is being held. They find the wolf house and free Hera, and stop the rise of the leader of the giants. Gaia is trying to awaken and if that happens it's bad super bad. The 3 of them stop the awakening of her for now.