‘Joe’ in this case is slang for a secret agent. This book, the sixth and latest (but not last) of the series is set in Slough House, the place where the British secret service discards its rejects, ‘joes’ who screwed up in some way. Some of them were set up, but it doesn’t matter. Their boss, Jackson Lamb, is a thoroughly unlikable character, who is also compellingly watchable. The book opens with a scene in which two of Lamb’s ‘joes’ are killed — but we don’t know which two. As and I others have pointed out, Herron is not strong on plot. But he is fantastic with characterisation, and Slough House is full of characters. The next book in the series is not due out until February 2021, which is a good thing because otherwise I’d be reading it right now.