Null Space is an altogether worthy sequel to The Ship, which stands up even better on a second read, where its little flourishes become more apparent. The story unwinds on a vividly imagined series of worlds along the length of Orion’s Arm, culminating in a proper galactic battle – what’s not to like? Its narrative draws one in right from the start, as a convincing and engaging cast of characters, some familiar from The Ship, others not, are assembled and fleshed out. Alexander makes inventive use of physics, astronomy, and not a little biology to convincingly underpin his narrative, marrying alien sentience nicely to parasitism along with the little comic touches we’ve come to know and love – his ships may fold space, yet must be navigated with difference engines and slide rules. There are some entertaining linguistic touches too. Under the surface lurk the usual serious questions: this book is particularly good on what aliens might or might not get about humans.