While investigating the possibility that an HIV-positive man was murdered by an embittered AIDs victim, Ballard (Callie Thorne) and Gharty (Peter Gerety) inadvertently dig up more information on the Luther Mahoney shooting. Elsewhere, the Waterfront Bar gears up for a big Christmas party, to which Bayliss (Kyle Secor) invites Cox (Michelle Forbes). And Munch (Richard Belzer) is unexpectedly reunited with his ex-wife, Gwen (Carol Kane), who is in town for the funeral of her mother, a much-despised literary agent. Author Peter Maas makes a cameo appearance as himself. ~ Hal Erickson, Rovi