As a woman admires the jewelry at an auction house, she attaches an electronic sensor to a countertop. Meanwhile, after Stafford gives the doctors their Christmas Eve assignments, Grace is called to the lobby by a patient who mentions her gangland reputation before collapsing.
Grace learns Constantine didn't refer the patient. From Grace's description, Constantine identifies him as Russell King, a jewel thief who left Chicago after his crew was killed for stealing in mob territory. Franco tells Grace that he referred King to her so he could continue his undercover work as a member of King's new crew, and that King is planning a big heist tonight.
King's daughter, Amanda - the woman who placed the sensor - learns he can't be released from the hospital, but she assures him the heist will take place, saying he's taught her well. Meanwhile, Stafford and Brett tend to Kyle Bennett, a toy store employee who got an antler stuck in his head when a display collapsed.
Constantine demands Grace take him to King's room. Constantine warns King that if he steals anything, he'll have to give the mob their percentage. King refuses to accept this.
Grace tells King he needs further tests. King says he's only doing the heist so Amanda can become an independent thief, noting he and Constantine share similar fatherly concerns. Grace had no idea that Constantine is a father.
When Stafford and Brett examine Kyle, he has a seizure that requires immediate surgery. As they operate on a conscious Kyle to determine which parts of his brain are afflicted, Kyle's childhood memories of a baseball game move Stafford to tears. Meanwhile, Constantine learns that King's auction house heist dovetails with the city's shutting down the local water mains, which will enable King's crew to enter the building from below.
When Grace asks Stafford about his reaction, Stafford reveals he and his now-late son once bonded over a baseball game, which prompted his tears. Grace then discovers that King is suffering from an abdominal aortic aneurism, which - if ruptured - will kill him in minutes, and that King left the hospital.
Grace calls Franco to warn him about King's condition, but King is already inside the water main. Grace tells Franco to get him out, heads to the heist scene, and sees Constantine passing cash to the city's water workers.
Amanda tells Grace the mains are filling with water, and Grace orders Franco to get everyone out or be drowned. Franco drags a collapsed King into the truck that serves as the thieves' command post. Grace opens King's chest, stops the bleeding, and sends King to the hospital in an ambulance, saving his life.
Grace's actions are the talk of the hospital's Christmas party. Flanigan suspects Grace is hiding something, but Stafford interrupts his interrogation and sends Grace home, then watches a classic Christmas movie with Kyle.
Grace goes to Franco's apartment, and they get intimate. Meanwhile, Constantine's gang tell him that King escaped, that Franco is working with King, and that Grace was at the scene.
Constantine is unconcerned about King and welcomes the challenge of dealing with Franco. Constantine also says he'll deal with Grace in his own time - but it's Christmas and everybody deserves one night of peace.