This latest tale in the Slough House series begins with a barn in Wales being set on fire. Two bodies are inside. 
Meanwhile, in London, Britain's head of the Secret Service, Diana "Lady Di" Taverner is being her usual manipulative self - wheeling and dealing with politicians to get more funding for the "spooks" before sacking Emma Flyte from her post as "Head Dog", in charge of the security staff at Secret Service HQ. Emma sums up Diana Taverner's scheming brilliantly with the line: "You'd burn down a city to save face."
At Slough House, the Slow Horses have a new member, Lech Wicinski. The reason for his demotion is far worse than any of the "crimes" made by the building's existing rejects who carry out all the boring jobs required to root out the various threats to the nation's security.
One of them, River Cartwright, is preparing for the funeral of his grandfather, a former head of the Secret Service but that event turns into farce as he spots his father, ex CIA agent turned mercenary, Frank Harkness with whom River and his boss, Jackson Lamb, has a score to settle. 
This is the 7th book in the series - there having been a novella "The Drop" which preceded it and two characters from that book feature in "Joe Country". 
Another Slough House inmate, Louisa Guy, receives a call from the wife of her dead lover, Min Harper. Min's son Lucas has disappeared and his mother wants her to use her intelligence connections to find him.
Various strands of the story spin out as Louisa takes a holiday in order to track down Lucas who is somewhere in Pembrokeshire. As she heads off on her mission, Jackson Lamb is informed that Frank Harkness and 3 European mercenaries seem to be heading to the same location as Louisa Guy. Keen to dish out justice to the man responsible for the death of one of his slow horses, Lamb sends River and 2 others to find out what the mercenary squad is up to.
As they set off for Wales, winter sets in and the action switches between snowbound Pembrokeshire and London as author Mick Herron gradually draws the multiple strands of the story together. 
This is not a stand alone novel as there are too many links back to previous books in the series, but the main characters are up to their usual tricks with politicians and civil servants (including the spooks) bickering and backstabbing on a daily basis. There are marvellous descriptions of London and the living entity that is Slough House. There are also delightful descriptions of the winter weather and how a single day's snowfall paralyses Britain's cities and countryside; the latter adding more problems to the dangers already being faced by River and his colleagues. Jackson Lamb is his usual caustic self while his long suffering secretary Catherine has almost reached breaking point. Throughout this latest tale, the reader can delight in the jet black humour which laces all of the Slough House stories. I love how Mick Herron can skewer Britain's high and mighty in a single sentence and along the way take sideswipes at the Brexit debacle and the machinations of politicians who only have their own interests at heart. A great addition to a wonderful series. Highly recommended.  

My thanks to John Murray Press and NetGalley for a copy of this book in return for an unbiased review. (Please note that I have already bought the previous 5 and a half Slough House books, so I'm a committed fan!)

Don't even think about reading this if you're new to Herron's Slow Horses series: too many plot trails, too many character arcs are carried forward from what has gone before. But for devotees, there are intriguing developments with PJ back on the scene, and as scarily obnoxious and self-serving as ever. 

I don't want to give away even hints of spoilers but will say that there are some painful deaths, a vast coincidence that ties the various plot strands together, and far too long spent chasing around snowy Wales for my taste with quick-switch cuts between the various hunters and huntees. 

Still, Herron's writing is just so sharp, snarky and blackly funny that I can forgive much; and his handle on realpolitik is spot-on as usual. And with a sudden revelation as the end, this series has bags more mileage - thankfully.