It’s not too uncommon for an SF story to split itself between different time frames separated by centuries, with the causal links between frames only gradually made apparent – M. John Harrison’s Light is a well-known example – but the odd structure of Adam Roberts’s Purgatory Mount still seems pretty bold, as does the novel’s shifting tone from Clarkean far-future SF to gritty dystopian naturalism to earnest moral debates about responsibility and atonement. We begin in that far-future on the kilometer-long starship The Forward, whose five crew members, all named after Greek g...