This is my favourite one in the series so far. From the perspective of a new character, Cora (she was a mermaid in her world), we go on what I would call, a treasure hunt. Rini, who is the daughter of a previously met character, comes to Earth and is looking for said mother. This 'quest' leads Rini, Cora, and other characters we have met, through different worlds - which is why I love it so much! I don't particularly read this series for the character or the plot, but for pure imagination that is the worlds McGuire builds.