A busload of fume-sickened school kids ... a gunman whose shooting spree claimed 19 victims ... a guy in an opossum outfit who bit a man dressed as a kangaroo. They and so many others all converge at ER. The gurneys keep rolling in a superlative Season 7 that includes Abby's reunion with her mother, a turbulent woman who suffers from bipolar disorder. Also making the rounds in the 22 episodes: Carter returns from detox, Abby goes back to square one in med training. Benton struggles to emerge from Romano's doghouse. Kovac confronts a mugger, Weaver reveals her sexual orientation and Chen refuses to reveal the father of her child. Meanwhile, Greene and Corday marry ... and live under the shaow of Greene's health crisis. Excitement, drama, suspense - the doctors are on call.