Percy Jackson & the Olympians: Lightning Thief was based on the first novel in Rick Riordan's five-book series. The sequel will be based on the second book, The Sea Monsters. The script is still in the early development stages, with no director attached yet.
Original cast member Logan Lerman will reportedly return for the sequel. The story revolves around the title character and his friends, who head under the sea to find the mysterious Golden Fleece.
Percy Jackson & the Olympians: Lightning Thief, which was released last February, pulled in $89 million at the domestic box office and another $137 million internationally.