The study looks into and compares three main contemporary sources describing the first pandemic in 542, also known as the Plague of Justinian—the secular historian Procopius and two church historians, John of Ephesus and Evagrius. The bubonic plague epidemic spreading from Egypt was the most destructive scourge of the Byzantine Empire during the reign of Emperor Justinian I. It had immense direct effects on demography, the economy, craft and agricultural production, construction work and foreign policy too, as large cities and coastal trade centres, including the capital where perhaps up to half of the population was lost to the disease, were the most afflicted. Although Procopius, John of Ephesus and Evagrius all came from different backgrounds and lived under different circumstances, their records and memories complement one another, helping to create a vivid and well-rounded image of the times. Procopius was measured and even impersonal, imitating Thucydides, and while he attempted to describe the symptoms, course of the disease and life in Constantinople as accurately as possible, the moralising John of Ephesus aimed to leave a warning for future generations and so was focused more on the emotional dimension of the tragedy he witnessed in the provinces he had passed through. Evagrius, who himself contracted the plague as a child and later lost his wife, relatives and some of his servants to it, left a brief account, but also precise and to the point. The sudden and unexpected arrival of the bubonic plague, its short incubation period, high fatality rate with no regard for gender, age or origin, as well as the lack of effective treatments and the impossibility determining the origin and/or causes of the disease, deeply shook the whole society, leaving scars on the human psyche and behaviour. A whole spectrum of feelings that are not completely unknown to us after our own experience with the recent pandemic—the initial hysteria and panic were replaced by fear for ourselves and our loved ones and the fear that funeral rites and burials would not be conducted—along with uncertainty, despair, mistrust, doubt, resignation, frustration and apathy can be identified in the work of these three authors, in their testimonies, experiences, varying examples and stories. The authors recorded not only ruthlessness, indifference, selfishness, a refusal to help or the desire to enrich oneself from the tragedy, but also left evidence of fellowship, cooperation and a selflessness among people.