Lillian is actually the Heart of Earth, its source of magic, and the Guardians have to protect her. Cornelia attempts to gain her sister's trust. Matt, Mr. Huggles, and Napoleon become the Regents of Earth. Cornelia is forced to babysit her sister while her parents are out for the night.

Will makes a deal with Prince Phobos, since only the heir to the Meridian throne can claim its Heart. Seeing as it has become part of Nerissa's power source, in exchange for freedom he is obliged to return the Heart. Will is having a rampage on Mandy at the swimming competition.

Phobos convinces the Guardians to release Cedric and Miranda for more protection. Meanwhile, as it is Halloween, the one night in the year when a Heart can be taken by force, the Guardians have to protect Napoleon, as he is Lillian's familiar. The race is on to keep Napoleon away from Nerissa, but thankfully the girls are able to walk around in Guardian form because of the holiday. Phobos tricks Nerissa and assumes control over her Seal. Meanwhile, Irma is forced to take her brother Chris, Lillian, and Blunk trick-or-treating, only to discover that her crush Andrew Hornby likes to trick-or-treat too. Irma gives Chris and Lillian a crash-course in how to get the most candy, using her own powers to help.