Strike is first to notice the young girl who we later find out is Zoe Haigh. As he emerges from the Red Lion & Sun, where he and Barclay had been conducting surveillance, his attention is caught by her distress and distinctive appearance (The Ink Black Heart, Chapter 22).

He follows her to Highgate High Street, at which point his phone rings and he answers a call from Katya Upcott.

Zoe turns right through the entrance to Waterlow Park …

… and, now upset and talking to someone on her phone, she walks through the park and sits down on a bench. Strike moves behind her and eavesdrops.

Zoe then exits the park, turns left down Swain’s Lane…

… and then comes to a brief halt between gates of Highgate Cemetery West and Highgate Cemetery East before setting off again, still followed by Strike.

From here onward the route they take becomes unclear. “He followed her for another twenty-five minutes, until she reached Junction Road, a long, busy street full of traffic. On she walked, past shops and offices, until she reached Brookside Lane.…” 

The quickest way to get from the cemetery gates to her destination on Brookside Lane doesn’t involve much of a walk along Junction Road itself, but maybe Zoe deliberately took a roundabout route.

The likely location of Zoe’s flat is on Brookside Road, rather than Brookside Lane, which is fictitious. [Zoe] “disappeared through a side door that Strike could tell would lead to the upper rooms of an irregularly shaped corner shop” (The Ink Black Heart, Chapter 22).

Later in the book, Robin becomes friendly with Zoe as they are both leaving the North Grove Art Collective. They take the direct route toward Junction Road, down Highgate Hill (The Ink Black Heart, Chapter 40).

They walk and talk and then turn into Junction Road …

… and pass a toy shop full of plastic figures in the window …

… before Zoe says goodbye and disappears around the corner to enter her flat via the side door.

This map shows the route taken by Zoe when she was followed by Strike:

This map shows the route taken by Zoe when she was walking with Robin:

Brookside Road is featured again later in the book. Strike waits in the car parked just outside while Robin goes inside to talk to Zoe.