Contains spoilers through the second episode of Slow Horses Season 6.

When Jackson Lamb calls “Blake’s grave” in Season 6 of Slow Horses, he is not simply suggesting a trip to a cemetery. The slow horses understand the message as much as die-hard fans do: they are in danger and must disappear, cut off phone contact, and meet in secret. But the place is real, Blake was real, and the code did not appear out of nowhere. Back in Season 1, when Hassan Ahmed’s kidnapping spirals out of control and Diana Taverner tries to pin the blame on Slough House, River and the other agents learn what that reference means in practice.

The Blake in question is William Blake, the English poet, painter and engraver who lived from 1757 to 1827. His work brought words and images together in an intensely personal vision of religion, politics and society. The author of poems such as The Tyger and London, Blake distrusted institutions and the certainties they imposed. He was not a spy and is not part of MI5’s secret past. His name entered the story because he is buried at Bunhill Fields, a historic London burial ground that became the slow horses’ meeting place.

Bunhill Fields is in Islington, close to the City, with entrances on City Road and Bunhill Row; the nearest Underground stations are Old Street and Moorgate. Its history is particularly rich. From the seventeenth century onwards, it was a burial place for people associated with religious movements outside the Church of England, known as Nonconformists. The writer Daniel Defoe and John Bunyan, author of The Pilgrim’s Progress, are also buried there. Blake, an artist who resisted easy categories, rests among others who kept their distance from the conventions of their time.

There is even a small story behind the grave itself. For decades, visitors to Bunhill Fields could find a memorial to Blake, but it did not mark the exact spot where he was buried. Researchers recovered the location, and a new gravestone was unveiled in 2018. Mick Herron’s references to the site in his books therefore predate that recent marker. The address, however, has always been Bunhill Fields, a short distance from Slough House’s shabby office and the official London where other agents decide the slow horses’ fate.

But why would Lamb choose Blake in particular? The honest answer is that the series gives him no sentimental or literary explanation. In Season 1, Lamb takes the agents’ phones so they cannot be tracked and, when asked where they should meet, says only that they know the place. The name comes in the next exchange: Blake’s grave. The code is introduced to the viewer in the middle of a pursuit, when returning to the office could mean falling into MI5’s hands. The meeting at the grave is also in the first novel, Slow Horses, although the book offers no definitive reason for Lamb’s choice. Blake is not a clue to the conspiracy; his grave is where the team knows to regroup when it needs to disappear.

The choice also invites a less practical reading, and here we enter the realm of interpretation. A burial ground historically associated with dissenters suits characters who have been pushed out of the centre of power. There is something of Lamb in a man who refused to let an institution tell him how to see the world, though it is hard to imagine the slow horses’ boss admitting to any poetic affinity. Blake’s London, viewed with suspicion in his poem London, also seems to speak to Herron’s city, where prestige and authority so often conceal corruption and cruelty.

In Season 6, the return to Bunhill Fields carries new weight. Former Slough House agents are being murdered, the team’s records have vanished from MI5’s systems, and a list of their names has fallen into the wrong hands. When Lamb discovers that even the paper files are gone, he tells Roddy “Blake’s grave”, orders him to pass the word along and insists that everyone go dark. He does not have to explain to the slow horses what to do with those words. What looked like an improvised survival plan in Season 1 now reveals itself as one of the few stable rules he has created to protect them.

That is what Blake has to do with the slow horses. He is not a hidden character in the conspiracy, but a real place that the series has turned into a secret protocol and a sign of belonging. When the code is activated, the agents know where to go and, above all, understand that they must trust one another. For people MI5 prefers to treat as expendable, it may be the most important meeting place they could have.