Luka pays the price for his misdiagnosis that left a patient with brain damage; Abby covers for an ailing Kerry; Carter pushes his way into Pratt's life after he's caught carrying a gun to work; Gallant tends to a recovering Harkins; Lewis refuses to allow the psych department to ignore the unsettling cause of a patient's crippling depression; a woman schemes against her dying husband; and Chen treats math students who overdosed on a stimulant.