London Rules is the fifth book in the Slough House series by prize-winning British author, Mick Herron. During a sweltering summer in Slough House, the slow horses perform, with a minimum of enthusiasm, the tasks their boss, Jackson Lamb has dreamed up: Louisa Guy scans library records for borrowers of possible terrorist texts; River Cartwright pretends to compare rate payments with the electoral roll to reveal possible terrorist safe houses, while he worries about his demented grandfather; and J.K. Coe composes fake emails for agents who need to disappear after interacting too closely with the general public.

Still on the wagon, Catherine Standish mops up after Lamb while also monitoring the psychological temperature of their reduced number, in particular: grief over those recently lost, the effect of (now-drug-free for 62 days!) Shirley Dander’s anger management course, the stability of the ever-silent, traumatised Coe, River’s concerns for the O.B., and Roddy Ho’s continuing over-inflated belief in his own popularity.

Meanwhile, in the real world, a terrorist attack on a Derbyshire village leaves twelve dead, a pipe bomb at a zoo has a similar death toll, and the discovery of a bomb on a train averts another potential disaster. As Regent’s Park searches for terrorists, First Desk Claude Whelan also has to cope with the PM’s demands for certain background checks, an MP with PM ambitions, the MP’s tabloid journalist wife and of course, his Second Desk, Lady Di Taverner, who has designs on his job.

When there’s an attempt on Roddy Ho’s life, the slow horses are at first incredulous, then puzzled. Coe seldom contributes, but when he does open his mouth, it’s worth listening, even if Lamb’s sharp mind is already a long way towards figuring it out. And once again, the slow horses are out on an op. Apart from a generous helping of snappy dialogue, fists, knees, elbows, a wrench, a knife, a coat-hanger, guns, a bottle of bleach, and a tin of paint come into play.

As always, Jackson Lamb is rude, inappropriate, sharp and sly. He has a lot of fun with addressing the unfortunately-named Devon Welles. This instalment sees the first of the London Rules, “cover your arse” adhered to by many players, and ultimately, Ho maintains his oblivion regards the general opinion of his appeal. The idea that “…Lamb will go to any lengths to protect a joe, but would watch in mild amusement if the rest of the world hanged itself” is soundly reinforced.

Herron’s plot is imaginative but easily believable, with the odd twist to keep it interesting; there’s plenty of humour, much of it black, that will have readers snickering, giggling and laughing out loud. This fifth instalment of the series, while it contains some spoilers for earlier books, can easily be read as a stand-alone, but with a series as entertaining as this one, why would you? Another excellent dose of British spy fiction.