In the distant future, a starfaring Neanderthal woman sits on a dock on the planet No-Moon, waiting to trade with the aquatic alien known as Second-Best Sailor. Her trading partner is late for their meeting, but that's not why Smiling Teeth May Bite is uneasy. May, like all Neanderthals, possesses a strong empathic gift and an impressive pattern-recognition talent. And her powers warn her that a grave, unnameable danger is heading for No-Moon.The threat is worse than May can imagine. The starships of the Cosmic Unity fleet are hurtling toward No-Moon, bearing religious missionaries disseminating the Memeplex of Universal Tolerance throughout the galaxy. If the inhabitants of a new world decline to convert to Cosmic Unity, their decision is not tolerated.Most readers won't be surprised by Cosmic Unity's bloody-minded missionary zeal, but Heaven offers some great surprises in its big ideas and its richly imagined alien races. Reminiscent of Hal Clement and Bruce Sterling, Heaven is a fun, thought-provoking, impressive example of classic sense-of-wonder science fiction. Perhaps this shouldn't be a surprise, considering the authors: Dr. Jack Cohen is a reproductive biologist and SF alien design consultant, and Dr. Ian Stewart is a professor of mathematics. --Cynthia Ward