At Regent's Park, the Intelligence Service HQ, new First Desk Claude Whelan is learning the job the hard way. Tasked with protecting a beleaguered Prime Minister, he's facing attack from all directions: from the showboating MP who orchestrated the Brexit vote, and now has his sights set on Number Ten; from the showboat's wife, a tabloid columnist, who's crucifying Whelan in print; and especially from his own deputy, Lady Di Taverner, who's alert for Claude's every stumble. Meanwhile, the country's being rocked by an apparently random string of terror attacks.

Over at Slough House, the last stop for washed up spies, the crew are struggling with personal problems: repressed grief, various addictions, retail paralysis, and the nagging suspicion that their newest colleague is a psychopath. But collectively, they're about to rediscover their greatest strength - making a bad situation much, much worse.