Amy is a young woman who has recently purchased a house, and is congratulated over the phone by her friend Jane. Amy seems distant, confusing Jane, who mentions that she cannot come over due to having to visit her sister in law’s birthday party, but agrees to visit anyway. Amy goes on her computer and begins searching for urns, before changing her search to leather jackets. When she visits, Amy reveals to Jane that she knows she is going to die the next day, which Jane initially writes off as a result of Amy consuming alcohol, revealing that Amy is a former alcoholic. Amy repeatedly says that she wants to be turned into a leather jacket after she dies, so she could be made into something of use. Jane leaves, telling her she will call the next day. Jane returns to her house to continue studying samples under a microscope, but suddenly becomes paranoid and rushes to Amy’s house, leaving several voice messages but being unable to contact her. She then leaves to go to her sister in law’s birthday party.
At the party, Jane appears disheveled and in her pajamas, confusing the other guests and disturbing them by saying she, too, is going to die tomorrow. This upsets Susan, Jane’s sister-in-law, while Jane’s brother, Jason, tries to defuse the tension. Tilly, a party guest, remarks to her boyfriend, Brian, that she thought Jane was crazy as they are in the car preparing to leave. However, Brian reveals he thought she was correct, revealing the two of them had also become infected. Jason and Susan are then infected while cleaning after the party, as they end up passing the fear onto their daughter. At a hospital, Brian kills his father by interrupting his life support systems, upon which Tilly reveals she was simply waiting for the death in order to break up with him. Jane goes to a doctor, who initially wants to refer her to a psychologist.
Amy goes for a ride in a dune buggy with a driver, during which she has a flashback to an event before the film started, in which she and her boyfriend Craig went to Craig’s brother’s vacation house for a weekend. During the weekend, the two order pizza, and it is implied that Craig became infected by the pizza delivery driver, setting the events of the film in motion. After the ride, Amy then passes the fear onto the dune buggy driver, before the two briefly attempt to make out, before giving up. Back at the doctors office, Jane passes the fear onto the doctor, who has a breakdown before leaving to be with his wife. Jane returns home and begins communicating with the bacteria she sees under the microscope in an attempt to calm herself, before seeing something enter her home that she asks “is this the end?”
Amy returns to the vacation home to find that Craig has committed suicide. The next morning, Jason and Susan discuss what they believe will be their final day, and agree to not wake their daughter so she can pass away in her sleep. Jane then wanders into the home of two young women, Sky and Erin, who seem unfazed by Jane’s bloodied appearance, before revealing they both have the sickness, as well. Jane asks to use the pool, and begins swimming as her blood soaks the water. Sky and Erin talk casually about what they will miss when they are dead. Amy then visits a leather shop, and begins asking questions about custom work, eventually asking about what they could do with ‘a mammal’. Amy begins tearing up as the employee describes the process, before jolting awake, finding herself lying on some rocks. She then begins whispering to herself, going between “it’s okay” and “I’m not okay”, before gently humming to herself as the film ends.