The Son of Neptune by Rick Riordan

The Son of Neptune is the second book in the The Heroes of Olympus series written by Rick Riordan. The Son of Neptune is the second book in the series and is preceded by The Lost Hero and succeeded by The Mark of Athena, which is to come out in the fall of 2012. The story The Son of Neptune follows the adventures of Percy Jackson, a demigod son of Poseidon, as he goes to Alaska to free the Greek god of death, Thanatos, and save the world from Gaia, the earth goddess.
The book The Son of Neptune received mostly critical acclaim, winning the Goodreads Choice Award in 2011 and landing on three bestseller lists. The book The Son of Neptune also uses Rick Riordan's new style of writing, third person narration, where the point of view switches between characters, in this case Percy, Frank and Hazel... The Son of Neptune begins with Percy Jackson being chased by the Gorgon sisters. They intend to kill Percy to avenge the death of their sister Medusa. Percy manages to escape and stumbles upon Juno, disguised as an old lady, who gives him two options: to carry her to the Caldecott Tunnel and across the little Tiber (although he is warned that after crossing through the river he'll lose the curse of Achilles) or to retreat to the safety of the sea and live a long, happy life. Percy chooses to carry her, and when he gets to Caldecott Tunnel he meets two other demigods: Hazel Levesque and Frank Zhang. While they cross the river, Percy Jackson sees Frank get caught by the Gorgons and controls the river to kill the Monsters... (Summary by Wikipedia)