March 2020. Pandemic. In a ghost-like Barcelona due to confinement, a homeless person is murdered while sleeping on the street. It will be the first of a series of crimes committed following the same pattern: always against homeless people, always while they sleep, and always with extreme violence. Agents of the Mossos d'Esquadra police force Quique Molina and Marga Muñoz, at odds with each other over something that happened in the past, will have the mission of finding a serial killer in the midst of a pandemic. A killer who acts like a virus: causing mortality and "infecting" other people who end up following his example. For this reason, the two agents will have to immerse themselves in the underworld of homeless people while Sergeant Molina's own life, in the midst of a divorce, is falling apart.