There are a lot of characters in these books, and they remain true to how they are portrayed in previous volumes. Yoshi is still trying to prove himself, because he feels his parents don't want him. Molly is a good leader, but worries that her skills will decrease all too soon. The Japanese sisters are learning a bit more English, and able to communicate with the group through Yoshi. Javi really steps up and tries to help Molly. Hank is a good leader for the CubTones, and Kim, Crash and Pammy are all very separate entities. Calvin, of course, is difficult to read, but Molly does try to figure out the mystery.

There is an online gaming component to these books, so many of the children's adventures have a distinct video game feel-- they travel around, have to fight monsters, and find gadgets that help them with what they are attempting to do. The first book in the series is by Scott Westerfeld, and the second by Jennifer Nielsen, but Jude Watson is able to maintain the same feeling and writing style that made these books quick reads.

Children who love science fiction series like Voyagers! Or Todd Strickland Mars: Year One will find plenty of action and adventure in the Horizon series, and the mystery will appeal to those who have finished The Thirty-Nine Clues or Infinity Ring series.