Tom and the others debate how to keep the dragons a secret, even as a rambunctious young "cloaking" dragon gets loose in town and pursues a friendship with a reluctant Alex.
Tom and Jun encounter unexpected dangers and are separated while exploring the Hidden Realm of dragons. Tom introduces Jun to the dragon world, and Jun bonds with a dragon of her own.
Tom and the Riders vow to help Thunder face the dangerous dragon who attacked the King's Realm: a fierce and unpredictable Snow Wraith who has made its way from the Ice Realm.
When the Riders discover that Magma Breather is very sick, the only way they can help is to sneak the huge and heavy dragon into the ICARIS infirmary without being caught by any of the scientists.