Ten-year-old Florence Opal has a secret hobby: she travels through time looking for mythical creatures and brings them to turn-of-the-century Boston for safekeeping in the Museum of the Unexplained. The museum curator coaches her on these expeditions and prepares her for a raid of Calypso Island, where her rival, Marvel, hoards mythical creatures and neglects them.When her closest companion, a magical bird named Edison, disappears and Marvel accuses the museum curator, Florence must figure out which of them is telling the truth. And she soon discovers that Edison isn't the only one in danger.