The Shadow Thieves by Anne Ursu

Charlotte's cousin Zachary is coming from "across the pond" to live with her family. Zee, as he is called, is an outgoing, talented soccer player. He fits right into life at her high school. He fits in better than Charlotte. But the students are getting sick at school. Zee shares that it happened at his school in London and Charlotte begins to wonder what is going on. When two strange looking men attack Charlotte and Zee, Mr. Metos, their English teacher, intervenes. Charlotte and Zee share their suspicions with Mr. Metos. Mr. Metos warns them of the shadow thieves and confirms their suspicions. Soon Charlotte and Zee find themselves swept up in a plot to overthrow Hades in the Underworld.

If you enjoy Rick Riordan's Percy Jackson and the Olympian series, you should find The Cronus Chronicles entertaining as well.

The Hunger Games by Suzanne Collins

Every year, the Capitol requires each district to send to representatives between the ages of twelve to eighteen to play in the Hunger Games. In the Hunger Games the participants fight to the death on national television. When Katniss Everdeen's younger sister, Prim, gets chosen in the lottery to represent District 12, Katniss steps forward to take her place. But Katniss has skills, she's been providing for her family for years using the knowledge her father taught her. The Hunger Games is Survivor with an edge!