Agent of the Queen

In the seventh book in the Windrush series, Jack is sent to infiltrate the Fenian Brotherhood, who are threatening to cause mutiny in the British Army. The journey will take him from deepest England to Ireland and across the Atlantic to the United States and Canada. Jack discovers that another nation is using the Fenian cause for its own ends, and gets involved in battles and intrigue. But what's most worrying of all is the involvement of Helen, Jack's old flame. What is she doing with the Fenians?