In the series finale of "The Mob Doctor," Grace's mom and Constantine are rushed to the hospital. Both are still alive, but in critical condition. Nate calls Constantine's phone, and Grace picks it up. She learns about the shooting at the bakery from him, and then prepares to observe her mother's surgery.
In the hallway, she runs into Agent York, who reveals that Constantine was the target of the hit. The agent starts asking Grace about what she saw before the shooting and if Nate might know more. Grace gives Nate a heads up that the feds are watching him and goes to see Dr. White.
Dr. White confronts Grace about her ties to Constantine and says he can no longer turn a blind eye to her mysterious disappearances. Even though Grace is the doctor that treats his diabetes, Dr. White says she needs to stay away from Constantine while he is being treated in the hospital.
Meanwhile, Agent York confronts Nate about his involvement with Constantine. York says that he has enough evidence to put Nate behind bars for 20 years. But if Nate helps with the investigation into the Nogales cartel, York will make all those charges go away. York also questions Ro Quintero and learns that Grace and Franco used to be an item. York confronts Franco about covering for Grace, and York says that he will be reporting Franco to the attorney general.
When Constantine gets out of surgery, Grace goes to see him. Luke is there, as well, but Grace barely pays him any attention. Grace has a singular mission: to learn whether Constantine killed her father, as Al Trapani recently told her. As they talk, Grace learns what many fans have suspected since the pilot: Constantine is her biological father. Grace confirms this with her mother, who has pulled through after surgery.
Franco calls Grace, and he tells her to keep mum and play dumb when talking to Agent York. While she is on the phone with Franco, Grace's mom has an embolism and dies, reducing Nate to a sobbing mess on the floor.
Grace, in her grief, tells Constatine that she's going to the feds. He tells her that Al Trapani is the one who deserves the blame for her mother's death, and she decides to take revenge. Constantine authorizes her to speak on his behalf, and she goes to Luke to find a way to contact the Nogales cartel without using Trapani as a middleman. Unable to say no to his sister, he agrees.
Luke and Grace meet with the leader of the Nogales cartel, who is just as upset at being played by Al Trapani as Constantine is. Grace tells him that Constantine is willing to give the cartel part of Trapani's territory in exchange for a truce. Additionally, they ask for the hit on Luke to be transferred to Trapani. The cartel leader agrees but says if things go south, Luke and Grace will become targets themselves.
Grace reports back to Constantine and learns that he lied to her about the terms of the deal, meaning she unknowingly fed lies to the cartel. In retaliation, she waits for Constantine to fall asleep, and then gives him an overdose of insulin, killing him. She walks out the hospital, where Franco is waiting for her in a car. The two kiss, and they drive off toward Mexico.