|Murder Can Be Contagious|
|Season 04, Episode 02|
|Air Date||September 26, 1996|
|Previous||Murder by Friendly Fire|
|Next||Murder on Thin Ice|
A burglar inadvertently becomes infected with a deadly virus. Dr. Sloan and Jesse are subsequently exposed to the virus after Jesse stumbles upon the thief's dead body. Both Mark and Jesse are confined to Mark's home while Steve and Amanda investigate the drug company that manufactured the virus, in the hopes of discovering an antidote before Jesse runs out of time.
While surfing, Jesse finds a dying man on the beach. Mark knows the symptoms from Guatemala, 1953, as smallpox: fatal, highly contagious and successfully eradicated. The beach house is quarantined and the beach cleared. An autopsy on the victim Eddy, a thief, shows it's a man-made mutation with an 8 hours incubation period. In his backpack Jesse finds only jewelry, including B.A.L. initialed cuff links belonging to robbed neighbor Brandon Lyndstrom, found murdered at his home, who was the CEO of biological research company Lyndscience. There VP Gayle Wentworth claims the virus could never have left the facility and invokes national security, but indeed all samples are missing from the safe. Jesse tells Mark, whose immunization is outdated, he admires how close he and Steve are, Jesse's dad is barely a rare postcard. Mark calls the FBI, which puts Special Agent Dunleavy on the case with Steve and 'informally' contacts the likely virus fence, Sebastian Dupré, who claims he 'must inquire'. A frantic Steve pressures Dupré the hard way, finds the thief Ray Dinino but he hasn't got the antidote. Jesse soon gets symptoms - making the antidote would probably take longer then the youngster has left, so Mark decides to inject himself with blood, hoping his immunity will be reactivated: even if it fails, he only loses a few hours. Then Jesse has an idea about the real owner of the expensive backpack.