When Robin’s brother Jonathan comes to stay with her for the weekend, he also brings his friends Kyle and Courtney. To Jonathan’s disappointment, Courtney seems to prefer Kyle to himself, with her and Kyle seen “giggling and whispering” to each other. 

Kyle is described as skinny and a couple inches taller than Robin with “a high-fade haircut, large, bloodshot eyes and a neatly groomed beard.” He’s also fairly inconsiderate, doing things like dropping his dirty bag on Max’s light-colored sofa and not offering to help take them to the other room. 

When he and Courtney later get into a heated debate with Strike over dinner, Robin notes that he has “the air of a young man who was used to being listened to.”

^{Troubled Blood, Chapter 40}