Wolfe Macfarlane is an unscrupulous man. As head assistant to Mr. K—, he abuses his position of authority to influence Fettes. When Fettes tells Macfarlane his suspicions about Jane Galbraith’s body, Macfarlane admits that all the bodies supplying the dissection tables have likely been murdered. He’s been living easily with the knowledge for some time and is only concerned with staying out of trouble. He counsels Fettes to not talk about or even think about it. Macfarlane’s murder of Gray further illuminates Macfarlane’s mercenary character. Gray is depicted as a bully with some kind of power over Macfarlane. Murdering Gray is a way for Macfarlane to get even, eliminate a threat, or simply eradicate a persistent wound to his pride. Regardless of the reason, Macfarlane’s murder of Gray shows the escalation of his depravity. 
 
Unlike Fettes, Macfarlane’s conscience does not appear to carry the weight of his past deeds. During their reunion at the George, Fettes is described as looking older than his former classmate, and Macfarlane is depicted as a handsome man, well-dressed, and prosperous. He clearly continued with medical school despite the events that drove Fettes away. When Fettes confronts him, the doctor once again tries to manipulate his old classmate. He tries to lure Fettes into giving him his address with the promise of money. However, once the story of their acquaintance unfolds, it’s implied that Macfarlane’s true goal is to go to Fettes’s home to eliminate the threat of exposure. When Fettes rebuffs his offer, saying he’d never take money from Macfarlane, the doctor only refrains from attacking Fettes in the lobby of the inn because of the presence of witnesses. It’s clear Macfarlane has not changed or repented but is still the same unscrupulous and evil man he’s always been.