The Heroes of Olympus
The second book in "The Heroes of Olympus", "The Son of Neptune", was released in October 2011. The third book, "The Mark of Athena", was released on October 2, 2012. The fourth book, "The House of Hades", was released on October 8, 2013. The fifth and final book of "The Heroes of Olympus" series, "The Blood of Olympus", was released on October 7, 2014.