What is the main theme in the novel, Ghost Train?

The unifying theme of Ghost Train is justice, with the spirit of a murdered man calling out for discovery and a resolution of the mystery of his disappearance during World War II. Although it is Remi who first recognizes that there is a mystery underlying the manifestation of the train, it is Niya who recognizes the need for justice and demands that it be found. Her desire for justice draws in social themes and ties them to the ghost train. Bitterly cynical about how blacks like herself have been treated, Niya wonders who in the 1940s would care about a missing, perhaps even murdered, black man?