Aaron and Jack join forces in operating on a man who sustained multiple fractures in a parachute jumping accident; Diane rejoins the staff as a teaching attending in internal medicine, and quickly draws a demanding and manipulative patient who's making the staff miserable; Kate's grief over her father's death is compounded when she's carjacked on her way home from his funeral and his ashes are not recovered with the car; Diane unsuccessfully seeks some moral support from Dennis and Philip; after Tommy tells her some hard truths about creating her own misery, Kate decides to take responsibility for the choices she's made, and starts by telling Peggy Harrod the truth about her daughter's death; Jack takes one on the chin when he gives the parachutist's would-be bride some bad news; Kate returns home to find the carjacker has returned her father's ashes while burglarizing her home; Philip has it out with Aaron and reaffirms his intention to keep Tommy from closing the hospital.

Diane is faced with a dilemna when she has an opportunity to examine a 500-year-old Incan mummy temporarily in town for an exhibition. An accident victim loses his memories but gains a much nicer personality, presenting Shutt and McNeil with a dilemmna.

Word of Billy's and Diane's engagement receives a mixed reception at the hospital; Jack returns from vacation with a windfall and a feverish belief he's on a winning streak; Kate alienates some colleagues when a reporter follows her around the hospital; Jack takes on the delicate job of operating on an infant with an exposed spinal cord.

Dr. Shutt views his life as a musical after he collapses from an aneurism.

Austin and NcNeil fly to London for a conference and are forced to perform lifesaving surgery with only an airline medical kit. Shutt begins his psychiatric residency.

Catera must operate on a 5-year-old who is suddenly stricken with seizures. An HIV-postive friend of Dr. Grad's talks to Diane about getting pregnant (she wants advice) and Diane (who discovered a lump in her breast) is afraid that neither of them will see their children grow up. A mother and daughter come into the ER handcuffed together.

Diane goes into labor unexpectedly and when no one can find Billy she reluctantly asks Kate to be her coach. Wilkes must get a family to safety from an abusive husband/father. McNeil and Catera take dance lessons (with special guest star Kenny Ortega, who choreographed ""Brain Salad Surgery."" Billy arrives at the hospital and discovers that Diane is having a c-section after her and the baby have gone into distress during the labor.

A poisonous gas is released in a bank and the doctors try to contain the gas, that is threatening many lives including Dr. Hancock.

During surgery to resolve an HIV-positive woman's post-partum complications, Diane accidentally cuts herself and is exposed to the virus; problems arise between Jack and Lisa when he discovers that she's been seeing Robert; a homeless man takes shelter in the hospital's main entrance; an unidentified man is hit by a train after trying to save a child; Jack takes up golf in the hospital.