Colette McVeigh is from a staunch IRA family; her husband was killed by the Brits and she and her brothers are active terrorists.
Arrested after a failed bombing raid, she's offered the chance to become a "tout" (informer); she accepts, so she can stay out of prison and bring up her children. But touts, if discovered, are tortured and executed with disgusting brutality. Her MI5 handler, Ryan, becomes more and more emotionally involved with her as she puts herself in ever graver danger.
It's a taut thriller which conveys the ugliness and cruelty of the time well; but much of the writing is boilerplate, with characters doing routine thriller-ish things – smoking cigarettes, drinking coffee, driving fast, looking at watches and, in Colette's case, sitting bolt upright in bed after nightmares, which no one ever does in real life.