Bob Minzesheimer

USA TODAY

The first four of the five books in Heroes of Olympus, Rick Riordan's latest adventure series for kids, have all landed at No. 1 on USA TODAY's Best-Selling Books list.

The cover of the fifth and final book, The Blood of Olympus, to be released Oct. 7, is revealed here for the first time.

Riordan, a former middle school teacher, has become a master at blending ancient mythology with modern adventure stories aimed at readers ages 10 and up.

His first series, Percy Jackson and the Olympians, which began in 2005, introduced a modern-day teen who struggles with dyslexia and ADHD and has an unusual father: Poseidon, the God of the Sea in Greek mythology. That makes Percy a demigod.

The Heroes of Olympus series, which began in 2010 with The Lost Hero, makes use of both Greek and Roman mythology. It features Jackson and other characters from Riordan's first series as well as introducing new ones.

Riordan's publisher, Disney, isn't giving away too much of the plot of The Blood of Olympus, other than to say that with Camp Half-Blood (for Greek demigods) and Camp Jupiter (for Roman demigods) on the verge of war, seven demigods travel to Athens to stop an army of giants from "raising the earth goddess Gaea and destroying human civilization."

Riordan says, "The Heroes of Olympus series has been such a blast — letting me expand Percy Jackson's world with a new cast of demigods. Saying goodbye to them in The Blood of Olympus feels like sending a child off to college. I'm sad, but I'm also proud."

His next series, to begin next year, is as yet untitled. It will make use of Norse mythology and be set in Boston, where Riordan, formerly of San Antonio, moved last year.