James Rollins is a paid-up member of the post-Da Vinci Code school of conspiracy thrillers. In The Judas Strain, this means turning Marco Polo's fabled journey to China into a modern-day mystery that threatens to destroy (you guessed it) the Catholic Church, along with most of eastern civilisation. The fourth instalment of his best-selling Sigma Force series, The Judas Strain features heroes who are suitably butch and have the requisite silly names: Painter Crowe and Gray Pierce. Rollins' leading characters have to crack a language predating Egyptian hieroglyphics, a device that suggests Hollywood pot-boiler Stargate as a major literary influence. This is bad, but not as bad as some of the writing. Not only do we witness 'evolution running in reverse, the oceans devolving into primordial seas', but we receive an extended lecture on cyanobacteria. Apparently the seas are reverting to the state they were in 100 million years ago. The reason? 'An unidentified slime. Something we haven't seen yet.' We then learn the United Nations has classified certain shellfish as weapons of mass destruction. And our heroes are worried about Marco Polo? What about the molluscs?