IN A SPECIAL CROSSOVER EPISODE, NEAL MCDONOUGH AND KELLI WILLIAMS FROM NBC'S 'MEDICAL INVESTIGATION' ARRIVE TO HEAD OFF MYSTERY DISEASE THREATENING NEW YORK -- RECORDING ARTIST WYCLEF JEAN GUEST STARS -- In a special crossover episode, Dr. Connor (Neal McDonough) from NBC's drama "Medical Investigation" and Dr. Durant (guest star Kelli Williams) from the elite N.I.H. team, are called into New York after a captured jewelry store thief who is AWOL from the Army displays unusual symptoms of an unknown contagious disease that is spreading fast -- and his accomplice is still on the run. Meanwhile, Cruz (Tia Texada) witnesses a gangbanger in her custody as he is gunned down by a 13-year-old boy and she senses a slick rival (as Marcel, guest star Wyclef Jean) is behind the murder. In addition, Yokas (Molly Price) has doubts about her former partner and a worried Carlos (Anthony Ruivivar) gets a pleasant surprise. Coby Bell, Cara Buono, Nia Long, Josh Stewart, Skipp Sudduth and Jason Wiles also star. DURING PART TWO OF THE "MEDICAL INVESTIGATION"/"THIRD WATCH" CROSSOVER EVENT, CONNER AND YOKAS WORK TOGETHER TO TRACK THE SOURCE OF THE MYSTERIOUS ILLNESS THAT HAS INFECTED PARAMEDIC CARLOS NIETO AND THREATENS NEW YORK CITY -- As the drama that began on "Third Watch" continues, the rest of the team joins Conner (Neal McDonough) and Natalie (Kellie Williams) in New York as they race against the clock to determine what the deadly virus is that has landed paramedic Carlos Nieto (Anthony Ruivivar, NBC's "Third Watch") and the robbery suspect that he was attending to in the ICU. Conner teams up with Detective Faith Yokas (Molly Price, NBC's "Third Watch") to search for the robber's accomplice, whom they hope will lead them to the source of the disease. Meanwhile, Eva (Anna Belknap) tries to console Holly (Yvonne Jung, "Third Watch") as she waits to learn if Carlos is going to live or die. As more infected people arrive at the hospital, the team must race against time to track the source of the mysterious illness before more patients die. Chris Gorham and Troy Winbush also star.