In Monster Mission, three children—Myrtle, Coral, and Etta—are dramatically kidnapped by some mysterious, mad aunts. But Myrtle, Coral, and Etta are far from killers—they need the children for a special mission. The secret island where they live is a sanctuary for magical creatures—mermaids, selkies, the amazing boobrie bird, and even the great Kraken himself—and the kidnapped children help to care for them. But what will they all do when the Island of Monsters attracts some dangerous villains, who want to turn it into a theme park?