Mackenzie “Mack” Carter is the one of the two protagonists and first-person narrators in the novel. Given Ferguson’s reliance upon the conventions of the A/B/O subgenre, Mackenzie falls within the omega category: a rare designation that is often ridiculed or stereotyped for its high libido and fertility. As a 29-year-old female shapeshifter, Mackenzie has been an ER doctor at Denver General Hospital for only one year. She is the granddaughter of Moira Carter. Though her father is still alive, he abandoned her as a child when her mother died because the grief of losing his mate rendered him unable to take care of her. Though Mackenzie grieved the loss of her mother, her father’s abandonment left her with lasting emotional scars that have made her reticent to find a mate of her own, despite her grandmother’s attempts at matchmaking.

Described as having “sandy brown hair and […] amber eyes” (13), Mackenzie is known to be a sociable and jovial individual who exhibits a keen intellect and saintlike behavior. This dynamic becomes evident when she agrees to participate in a fake relationship with Noah. She has cultivated friendships with many of her fellow medical staff members, such as Priya and Liam, and has been best friends with Parker for over 16 years.