This book which is set in 1915 and its main protagonist is Sebastian Wolff a Lieutenant in the British Navy, who is on secondment to the new Secret Service Bureau, a precursor to MI6. He has been given a new mission by his chief to go to Norway and then onto Berlin and to use his social skills to strike up a friendship with Sir Roger Casement. The Irish traitor is trying to arrange for German help in arming a Irish battalion to fight the British in Ireland, which was part of the UK then. Wolff is also to hunt down an enemy, a German/American doctor who is being trained to develop biological weapons to kill British interests.

The doctor, Dr Anton Dilger, has been persuaded by German high command that he would be saving his country men's lives by helping to shorten the conflict by using his medical skills in promoting biological warfare.

At that time the US was neutral but was selling a lot of armaments and horses to the UK as mechanised transportation was still relatively new and expensive. These biological weapons were intended to kill all the horses slowly as they crossed the Atlantic and if the dreadful diseases were passed onto their grooms and other attendants so much the better. The Germans were using disaffected Irish dock workers in the USA to infiltrate ports where horses and armaments were being shipped from and Wolff is also supposed to stop this.

The author builds up the readers sympathy for both Dr Anton Dilger in his fight for an end to the suffering of his nation at war and Sebastian Wolff in pursuit of a just end to the possible infiltration of the UK naval bases by renegade Irishmen with biological weapons. Although it is set in 1915, at a time when horses were used more than tanks and mechanised transport, the biological warfare aspect makes it seem a much more modern warfare. Wolff has romantic diversions with an adulterous affair he is pursuing in London and a much more chaste relationship he is having with an Irish girl in New York.

I really enjoyed this very exciting but fast-paced thriller, with intricately researched details about biological warfare. The story also featured plausible and sympathetic characters, on all sides of the conflict, and dealt with moral problems of loyalty, love and behaviour, which are relevant today. The narrative style, with Lee Child-style short chapters moving between the different perspectives of the characters perhaps owes something to the author's documentary background but added tremendously to the build up of tension and I was gripped until the final page. Well recommended.