The Mark of Athena by Rick Riordan

Wow, what a great ride.  Unfortunately, it ends with an enormous cliff hanger for Jason and Percy, the Roman and Greek versions of a myth.
This story begins where the previous book left off with the trireme from Camp Half Blood moving toward New Rome nestled somewhere in the Oakland hills.
New Rome has just finished a mammoth battle with the Gaea's forces as they continue to try to resurrect her from her banishment.
Well, things go wrong, of course, otherwise the story would be over.  They begin a new quest, no surprise, but Riordan continues to pump out good stories.  He reintroduces us to some of these ancient myths and legends throughout his stories.  I finally downloaded a copy of Bullfinch on my kindle to begin reading these old myths.  You may also want to look for a copy of Ingri D'aulaire's Greek Myths.
This is longer than some of his other books in the Percy Jackson or Heroes of Olympus series.  This is about as long as the Kane Chronicles.  However, sometimes the Kane Chronicles drag, not this series.  I read this book in a few days.
When does the next one come out, so I can check on my favorite heroes?