Melissa Marr’s “Seven Black Diamonds” is a modern fairytale that mixes the thrum of legend with potent questions about the environment.

When a human ship hits her in the sea, the faery queen Endellion loses her baby daughter and heir in the polluted water, and she begins a war against humanity that lasts generations. In the vanguard are cells of faery changelings, planted in human society in order to destroy it from the inside. One of these cells is the Seven Black Diamonds, seven part-faery teenagers brought up by human parents. All of them are members of huge crime families or American aristocracy, living in a modern world polluted but brimming with decadent glamour.

The war isn’t about only the queen and her lost heir but framed in terms of eco-awareness. The faery terrorists are, quite self-consciously, environmental extremists. Lilywhite Abernathy, the newest Diamond and immensely capable protagonist, is supposed to help lead her peers in the fight against the polluting force of humanity.

Problematically, she has no idea who she is or what she’s supposed to be doing.

Melissa Marr (Courtesy of Harper)

There are lovely subtle touches in this novel. A trickle of Gaelic links the faery courts to Scotland. But, there are subtle problems, too. Chief among them is the narrative handling of belief. In any extreme cause, it’s reasonable to expect that some of the participants really believe in what they’re doing. None of the Diamonds, though, is a true believer. They only fear the Byzantine consequences that will crash down on them if they fail the Queen. This may make the seven teenagers close to blameless and maybe more empathetic, but the absence of that real darkness makes the story sometimes seem bland.

This shying from real moral culpability affects the central romances too. What makes great romance is difficulty, and although there are superficial political barriers keeping many of the couples somewhat apart, there are no emotional or ideological chasms. Despite the great emphasis on divisions, none of the couples is separated by belief; no one who believes passionately in the faery cause is in love with someone who passionately hates it. Without that tension, this magical novel feels emotionally distant, a world away.

But Marr’s book is much broader than the environmental and political concerns at its center. The forces that really move all its characters are monarchy, family and magic.

Natasha Pulley is the author of “The Watchmaker of Filigree Street.”

Seven Black Diamonds

By Melissa Marr

HarperCollins. 381 pp. $17.99