Against a backdrop of corporate and political intrigue, environmental and cultural pillaging, and the unraveling of the very fabric of reality, an assassin, a knowledge broker, and a “conjure man” betray, bedevil, and bewilder each other and the powers behind the far-flung, watery outpost of Greene’s World.

There’s a lot going on in “Undertow,” and sometimes a bit too much. The book is rich with ideas about space travel, the interactions between humans and other species, the implications of ubiquitous cybernetics, and the manipulation of chance. Add in some fast-paced adventure, an intriguing setting on a watery world, and layered political manipulation, and it can be a lot to keep track of. It does pull together in the end, though, and the final chapter is riveting.

I especially liked that the aliens were truly alien, and not just people in funny costumes. Based on the biology of Earth amphibians, their drives, culture, and behavior are understandable, but clearly not human, and the failure of humans to understand them, and their very different sense of community and history, propels much of the action.