When M15 officer Liz Carlyle is posted to Northern Ireland, her heart sinks at the thought of working in a backwater. From the moment she arrives in Belfast danger follows and she soon discovers that the peace process in the province is precarious.
Then a source reports strange activity at a house in the Irish Sea owned by The Fraternity, an organisation Liz suspects of being a front for renegade former IRA men. Its head is Seamus Piggott, an Irish-American with a gun-running past. Then another informant reports that a plot is being hatched against the security forces. Liz and her colleague Dave Armstrong suspect Piggott is involved, along with a former French Intelligence officer.
Travelling to Paris, Liz pursues this connection with her counterpart in French Intelligence. While she is away, Dave Armstrong decides to take matters into his own hands. When Dave goes missing, Liz fears the worst, especially when she discovers that the obvious suspects have all disappeared.