When a former solider killed by a very contagious strain of the smallpox virus, the Hawaiian Governor tasks Five-0 with uncovering the source of the virus and preventing an island-wide outbreak. Max thinks that the victim was injected with the virus as a part of a clinical trial for anti-depressants, so Danny and Chin Ho investigate and eventually find the trial project manager's dead body in his home. They also unearth a print at the crime scene belonging to Dracul Comescu, a man who has a long history with the NCIS: Los Angeles team. Danny puts in a call to Special Agents Sam Hanna and G. Callen, mentions Comescu, and they jump on the next flight to Hawaii to help with the case. They determine that Comescu is arranging to sell the smallpox virus to a buyer at the International Marketplace, so they stage a sting operation to take him down. Callen is forced to shoot Comescu as he reaches for a vial in his pocket, killing him instantly and preventing him from More...unleashing the smallpox virus. However, Kono later learns that the vials Comescu was carrying weren't actually smallpox; that someone had switched out the vials and the real virus is still out there. They discover that the switch was made by Jarrod Prodeman, a doctor involved in the research, and that he just landed in Los Angeles with the smallpox...