Set in the morally grey world of assisted suicide, Mary Kills People is an intense, controversial, and thought-provoking drama. The series follows Dr. Mary Harris, a single mother and emergency doctor by day, who also moonlights as an underground angel of death — helping terminally ill patients who want to die and slip away on their own terms. So far Mary has managed to stay under the radar; but business is booming, and her double life is getting complicated. When her world starts to unravel, Mary realizes she's going to have to fight dirty if she's going to stay in the killing game.
It's been eight months since Mary and Des framed Grady, their drug dealer, for the deaths of their patients. While Des has been serving prison time to protect his partner, Mary's been managing surprisingly well on her own – she's found a new supply of pentobarbital in Mexico, her business has continued to thrive thanks to Annie's ability to source terminal clients in need, and her ex-husband Kevin has moved in and taken on half the parenting duties following a messy break-up with Louise. Though Jess still suspects that her mother is hiding something, Mary has been working diligently to keep her professional and private lives separate. But secrets can only be hidden for so long when Olivia – a mysterious woman with a connection to Mary and Des – comes to them with a deadly request.
Following the disappearance of Travis, Des worries that he and Mary may have crossed a moral line from which they can never return. After jeopardizing Ben's investigation of Olivia, Mary tries to make amends, which has repercussions for a patient in dire need.