Spy thrillers set during World War I are not that common but spy thrillers, wherever set, as intelligent and well-written as The Posion Tide are positively rare. Andrew Williams has shown in previous novels The InterrogatorTo Kill a Tsar that he is good at handling big historical themes as well as small historical detail and The Poison Tide is his most ambitious book to date. As the Great War rages in the mud and blood of the trenches on the Western Front, another, quieter but just as deadly, war runs in parallel between the newly-formed intelligence networks of Britain and Germany. On the British side, officer and gentleman Sebastian Wolff is recruited by spymaster "C" (the forerunner of James Bond's "M")and whilst he shows a natural talent for the dirty side of the spy trade, he is always conscious that what he is doing out of loyalty for his country is eroding every decent thing he was brought up to believe in. His initial objective is to travel undercover to Berlin and spy on Sir Roger Casement, the Irish Nationalist co-operating with the Germans in order to throw the British out of Ireland. When his mission takes him on to neutral America to infiltrate the pro-Irish independence movement there, Wolff stumbles on an operation run by German Intelligence which is far more terrifying than the prospect of an uprising in Ireland (which happened in 1916). In fact, it is nothing less than the development of the first true Weapon of Mass Destruction. The historical background is fascinating and totally believeable, the plotting is tight and the narrative pacy for a book of this length, but what shines out is Williams' grasp of character. When the hero accidentally kills a friend rather than a foe his grief and self-doubt are heart-achingly well-done, as are the scenes of teh spy falling in (and out) of love and when the British "traitor" Sir Roger Casement comes to realise what a tragic, impotent figure he really is. If you are looking for a slam-bang, shoot-'em-up spy yarn, look elsewhere. This is a very clever, very satisfying, very well-written thriller.