This is the second book of the "Percy Jackson Series". Published on June 1st, 2006.American publication date: April 1, 2006
UK publication date: July 1, 2006
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 magic item powerful to save the camp before it is overrun by monsters. The catch: they must sail into the Sea of Monsters to find it.
Photo: Google images