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 paranoid concerns of David Cartwright, a Cold War-era
operative and one-time head of MI5 who is sliding into dementia, and
questions his grandson, River, must figure out answers to now that the
spy who raised him has started to forget to wear pants. But River,
himself an agent at Slough House, MI5's outpost for disgraced spies, has
other things to worry about. A bomb has detonated in the middle of a
busy shopping center and killed forty innocent civilians. The "slow
horses" of Slough House must figure out who is behind this act of terror
before the situation escalates.