Most viruses do no harm to humans - and, as this fascinating book explains, a large class of them might even prove our saviours ... [Phages] regulate our gut microbiome, are crucial to marine ecosystems, and inspired the modern Crispr technique of gene-editing ... All this and more is thrillingly recounted in Tom Ireland's superb book. This is real luxury-class science writing, exploring how a "Stalin-tainted" idea from long ago can be rehabilitated, alternating scientist interviews and vivid case studies of miraculous-seeming cures with historical narrative and limpid biotechnological explanations ... He also demonstrates excellent comic timing. Steven Poole Telegraph