Just as Clara and her sister are settling into their new life, Drosselmeyer sends a desperate message to the Seelie Court. With Lir and Louisa occupied elsewhere, Clara and Finias (the Sugarplum Faerie) have no choice but to respond and forge deep into Unseelie Territory, where a cruel Queen, known as the Eater of Hearts, has taken the throne. As they infiltrate the Court of Dread, Finias and Clara are forced to keep their relationship a secret. Meanwhile, the ravenous victims of the Queen, called the Heartless, turn the Unseelie kingdom into a far more dangerous place than usual.