When a torrential rainstorm pounds Chicago, patients stack up while Dr. Weaver speeds to an accident site where a pregnant woman lies injured inside a wrecked ambulance while live power lines spark -- until heroic first-year resident Gallant makes a dangerous leap of faith. Elsewhere: a shaky Dr. Benton gets the lab reports that will determine if he is the father of his son Reese; Kovac's new girlfriend gets in trouble and gives him some unexpected news; Dr. Carter is shocked to see his grandmother wheeled in after breaking her hip in a hit-and-run car accident which injures a young woman -- and Dr. Greene tends to a guilt-ridden boy who feels responsible for the disappearance of his younger brother after playing in a flooded river.