Who do you think the new character in the Mark of Athena will be?
According to Rick's site, a totally new character will be released some point in September.
So far I am betting an entire stock of blue chocolate chip cookies (courtesy of Percy's awesome mom) that the new character is a girl and a daughter of Neptune.
BUT- The Doors of Death remain a mystery. Perhaps this new demigod is exactly the person we were looking for to close them?