With how “Slow Horses” had been progressing, season 4 episode 5 would be one of those set-up episodes that also turns out to be make or break. All the chess pieces slowly start to move across the board and set themselves up for a confrontation, or, as Harkness states in the opening segment of this episode, “calling hello on the way.” It all converges with an action sequence that recalls the fantastic action-heavy last season.

Slow Horses (Season 4) Episode 5 “Grave Danger” Recap: Where does Harkness go to gather information and regroup?

Suppose the primary question had been how Harkness had been able to gather information about Chapman and Cartwright. In that case, we are afforded the answer this week when Harkness visits the apartment of the librarian of the Park’s archive, Molly. We learn that Harkness had been essentially catfishing her for a week by presumably taking on the cold body identity of Mitch Philpott.