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)

The Throne of Fire by Rick Riordan

The Throne of Fire is a 2011 fantasy adventure novel based on Egyptian mythology written by Rick Riordan. The Throne of Fire is the second novel in The Kane Chronicles series, which tells of the adventures of modern day fourteen-year-old Carter Kane and his thirteen-year-old sister Sadie Kane, as they discover that they are descended from the ancient Egyptian pharaohs Narmer and Ramesses the Great.
The Throne of Fire was released on May 3rd, 2011. The book The Throne of Fire takes place roughly 3 months after the first one.
Ever since the gods of Ancient Egypt were unleashed in the modern world, Carter Kane and his sister Sadie have been in trouble. As descendants of the House of Life, the Kanes have some powers at their command. But the devious gods haven't given them much time to master their skills at Brooklyn House, which has become a training ground for young magicians. And now their most threatening enemy yet—the chaos snake Apophis—is rising. If they don't prevent him from breaking free in a few days' time, the world will come to an end. The story begins with Carter and Sadie breaking in to the Brooklyn Museum during a wedding to search for the Book of Ra, which will allow them to speak with Ra to help them imprison/kill Apophis the lord of chaos. Along with them are Khufu the baboon, and their new trainees, Jaz and Walt. Instead, they find a papyrus scroll that is booby trapped with a series of fire traps. As Carter and Walt distract the demons that are apart of the booby trap, Jaz perform a spell that banishes the demons back... (Summary by Wikipedia)