Which book series from Rick Riordan do both the fantasy novel The Hidden Oracle and the Camp Half-Blood-Chronicles have in common?
The Hidden Oracle: The Hidden Oracle is a fantasy novel based on Greek and Roman mythology written by Rick Riordan. The Hidden Oracle:  It was published on May 3, 2016, and is the first book in "The Trials of Apollo" series, the second spin-off of the "Percy Jackson & the Olympians" series.
i don't know