On a recent whale watching trip off San Francisco, I was stunned by the immensity of the sea. The image of the fathomless sea so ubiquitous that it has ironically lost its power, but when you're on a thirty-boat floating above the continental shelf, squinting at two humpback whales off the starboard side, you are quickly reminded that we know very little of the larger half of our world.The idea of an underwater world that has escaped discovery by humans is not a new one, but it's also one that still holds a great deal of power. Helen Dunmore was inspired by the story of the Mermaid of Zennor to create a Cornish tale of a modern girl and boy, Sapphire and Conor, who are drawn into this underwater world, a world where they might just find they have a heritage. The waters of Ingo are tempting, however, and they may not have the strength to return to the world of Air. Mermaid Chair in Zennor Church (Photo credit: JohnBurke)The Mer of Ingo are enigmatic and slightly sinister. Dunmore uses their voices to deliver a strong environmental message, but the Mer's knowledge of humans belies their claimed lack of curiosity in the doings of our world, creating a dissonance that pokes at the reader's distrust.We see Ingo through human eyes, so other than a few moments were the characters are shown how to open them, there is little description of the wonders of the underwater part of our world. I found this a bit of a disappointment as I read the novel, but as the pages turned, the plot revealed that this lack of description was purposeful and as we travel deeper into Ingo in subsequent books, we may see more of those wonders as we travel though that ultimate mystery that we call our oceans.This review also appears at Boxes of Paper.