According to
The Hollywood Reporter, Nathan Fillion will play Hermes in the Thor Freudenthal-directed sequel titled
Percy Jackson & The Olympians: The Sea of Monsters:
"The star of ABC's Castle has joined on to star as Greek diety Hermes in Fox 2000's sequel Percy Jackson & The Olympians: The Sea of Monsters, based on the second book in Rick Riordan's best-selling young adult book series."
Logan Lerman will reprise his role as Percy, and Brandon T. Jason and Alexandra Daddario are also returning. Film is set to hit theatres in 2013. Here is a synopsis of the second book:
When Thalia's tree is mysteriously poisoned, the magical borders of Camp Half-Blood begin to fail. Now Percy and his friends have just days to find the only magical item powerful enough to save the camp before monsters overrun it. The catch: they must sail into the Sea of Monsters to find it. Along the way, Percy must stage a daring rescue operation to save his old friend Grover. He also learns a terrible secret about his own family, which makes him question whether being the son of Poseidon is an honor or a curse.