In the book The Son of Neptune the first main character Percy [Jackson] finds his way to a roman camp after being chased by gorgans who will not die. When he gets to the camp he helps a old lady who is actually Juno (Hera in Greek)! The second main character is Hazel, Hazel died in 1942 but Nico De Angelo son of Pluto (or Hades in Greek) brought her back. Hazel blacks out when she thinks of her past life. Hazel also has a gift that brings precious gems like diamonds to the surface but all the gems are cursed! The third main character is Frank he had always dreamed of being an archer but after he had led the three into battle he was claimed by Mars (or Ares). Frank's mother died in Afghanistan a few weeks before he came to camp.
Mars has issued a quest for the three heroes to save Thanatos the god of death in the lad beyond god or Alaska.