What happens when an old spook loses his mind? Does the Service have a retirement home for those who know too many secrets but don't remember they're secret? Or does someone take care of the senile spy for good? These are the questions River Cartwright must ask when his grandfather, a Cold War-era operative, starts to forget to wear trousers and begins to suspect everyone in his life has been sent by the Home Office to watch him. But River has other things to worry about. A bomb has detonated in the middle of a busy shopping centre and killed more than forty innocent civilians. The agents of Slough House have to figure out who is behind this act of terror before the situation escalates.