Dr. Mary Harris has a secret — beneath the surface of being an ER doctor and loving mother, Mary is also Dr. Death, helping terminal patients end their lives. She and her partner Des have been operating covertly for almost six months. However, a series of unforeseen circumstances, beginning with the unexpectedly complicated assisted death of superstar football player Troy Dixon, conspire to tear Mary down. Meanwhile, her greedy ex-husband Kevin introduces her to his new girlfriend, she discovers that her 15-year-old daughter’s wild BFF is into heavy drugs, and Mary ends up seducing a patient who is not who he seems.

After having sex with her patient Joel, Mary has second thoughts about helping him end his life. But when Mary discovers Joel is in fact Detective Ben Wesley, she has to scramble to dump the evidence, which greatly compromises their next gig. When a client’s teenaged son pulls a gun on Des, Mary is forced to approach Des’s dangerous drug supplier Grady Burgess for more pento in order to complete the job. Meanwhile Kevin’s relationship with a new woman intensifies and Mary realizes she may be losing her grip on her family.

Mary confronts Ben about being an undercover cop — beginning a game of cat and mouse as she doubles down on her cover story as an end-of-life-counselor. Mary’s personal life becomes even more precarious when she is blackmailed into helping Grady break a patient out of the hospital before he’s killed or imprisoned. Meanwhile, Jess’s relationship with Naomi is further strained when she discovers that Mary may be connected to Naomi’s drug habit, and Ben and Frank get a new lead when Carly (Troy Dixon’s widow) appears to be hiding something about his death.

Ben attempts to get closer to Mary who, still feeling unsafe after the Grady incident, visits her sister Nicole at their childhood home. But when Ben follows her, a much-needed moment of respite turns into an honest heart-to-heart until Ben discovers something startling about Mary’s past. Meanwhile, Grady finally puts the pieces together about Mary’s operation and approaches her with a surprising offer. After meeting Morgan, a potential client with cystic fibrosis, Des becomes an unsuspecting victim of circumstance and police misconduct, forcing him to make a difficult decision that could destroy Mary.

Mary’s world starts spinning out of control when Annie quits the business and Des decides to take Frank up on his offer to turn on Mary in exchange for leniency. After Jess finally calls Mary out on all her lies, she has a ‘dark night of the soul moment’ while tending to Morgan, the patient with cystic fibrosis. For the first time Mary questions her choices and confronts how much her mother’s death shaped her life.

To get the police off her back once and for all, Mary has no choice but to convince Grady that she’s accepted him as a partner. But in reality, Mary has hatched a plan to frame Grady for all the suspicious deaths in her wake — the only catch being that she’ll have to kill him for her plan to succeed.