On a busy Halloween night, Carter and Abby are the only staffers in costume when victims of an apartment building fire pack the ER. Corday takes on a new med student for a surgical rotation - Paul Nathan, who suffers from Parkinson's disease and decided to pursue medicine after being diagnosed. Despite a difficult first day, both professionally and medically, Nathan makes a difficult diagnosis. Romano's rehab lags behind his expectations, and he begins to think his role in surgery is no longer an option. In a moment of personal weakness, he tries to express his feelings for Corday. Weaver continues to display erratic behavior, raising staff suspicions about her menopause. Luka's burgeoning sex addiction worsens, as an affair with Chuny is revealed, and tensions rise when he treats a patient with a perpetual erection.

Corday clashes with new surgical resident Paul Nathan regarding his intervention into the treatment of a sickly young woman, Alison, who has signed a "do not resuscitate" order. Abby wonders about the erratic behavior of her visiting brother Eric, and feels conflicted over a nurse's official complaint against Kovac, Abby's former lover. Meanwhile, Pratt comforts Chen after a patient threatens her, and Corday suspects that an unconscious 14-year-old female patient has been sexually assaulted.

Abby fears the worst when her brother Eric suddenly disappears. He is actually AWOL and she forges Carter's name to obtain his medical records. Carter and Chen treat a frightened Chinese immigrant nanny, Tong-Yi, whom they suspect was impregnated by her employer. Meanwhile, new surgical resident Paul Nathan, who is struggling to overcome a physical disability (Parkinson's disease), tries to help in the emergency room but his fellow doctors do not appreciate his advice to patients. Unable to quench his sexual appetite, Kovac also gets into trouble in his professional life, despite his admirable resolve to find an eye specialist to treat a young gunshot victim. Gallant and fellow medical student Erin Harkins engage in an escalating competition of medical knowledge. And Weaver gets some much-needed good news.

Abby's family nightmare continues as she searches for her missing brother Eric, who she suspects is suffering from serious mental problems. Gallant accompanies her to his military base where they find Maggie, whom Eric turned to for help. When he's transferred, Abby and Maggie go to a Midwestern air force base, hoping to prevent Eric from being court-martialed for being absent without leave. Carter struggles to get out of Chicago to join Abby. Meanwhile, Corday treats a family of patients who, while building a snowman, were severely injured after being struck by a truck driver. She must help the father, Stuart, make a life-or-death decision. Corday also sympathizes with troubled surgical resident Paul Nathan as he struggles with the increasing symptoms of his physical handicap.