A young couple trying to reunite amid a city ravaged by a plague that turns its victims into deranged, bloodthirsty sadists.

After a year of combating a pandemic with relatively benign symptoms, a frustrated nation finally lets its guard down. This is when the virus spontaneously mutates, giving rise to a mind-altering plague. The streets erupt into violence and depravity, as those infected are driven to enact the most cruel and ghastly things they can think of. Murder, torture, rape and mutilation are only the beginning. A young couple is pushed to the limits of sanity as they try to reunite amid the chaos. The age of civility and order is no more. There is only "The Sadness".

In Taiwan, doctors warn that the Alvin virus may mutate and become dangerous for the population. But it is election year, and the political authorities minimize the menace to avoid a lock down and win the election. The young couple Jim and Kat are discussing their vacation on the next week, since Kat is stressed and needs vacation, but Jim has a meeting with a German agency in the period scheduled by her. Jim takes Kat to her work in his motorcycle, but when he returns, he stops at a cafeteria nearby his home to drink a coffee. Out of the blue, a client is wildly attacked by an old woman and soon the place becomes a havoc, with violent clients attacking the others that become also violent. Jim runs to his apartment and is attacked by his next-door neighbor, Mr. Lin. He has two severed fingers by Mr. Lin, but succeeds to escape. Meanwhile, Kat is commuting by subway and out of the blue, a man stabs and infects many passengers, and the begins a wave of violence in the wagon. Kat flees from the train with the commuter Molly, who lost one eye stabbed by a passenger. They reach the hospital, but Kat loses her cellphone during the running. She borrows one and tells Jim where she is. Soon they are attacked by a horde of insane people in the waiting room. Kat seeks refugee in the maternity section and is helped by the virologist Dr. Alan Wong. He explains to her how the virus infects the people but cuffs her to the shower while Jim seeks her out in the hospital.—Claudio Carvalho, Rio de Janeiro, Brazil