Cold is set in 1959 at the Common Cold Unit where, for almost 40 years, volunteers were "given" a cold by the staff, then had its effects studied in an attempt to find a cure. There was no shortage of applicants and people came back year after year. For some it was a free holiday; they were unpaid but given "pocket money".

The heyday of the Common Cold Unit was in the post-war period. Despite the holiday atmosphere, volunteers got a stern lecture and were expelled if rules were broken or they lied about their medical history or age.

Barry, a union official who likes the sound of his own voice, has been coming to the unit for years. When his room mate, John, is accused of breaking the 30ft rule, where volunteers are not allowed to get within that distance of anyone other than medical staff and room mates to avoid infection, he is asked to leave by his doctor. But Barry knows that John is innocent and goes into battle for him. It is soon obvious that Barry's fight with the establishment may be as much to do with his own feelings of insignificance. Even if he doesn't quite manage a revolution, he does get an apology out of the doctor, and he manages to attract the attentions of Lillian, another outsider at odds with the staff and her own room mate. Before long Barry breaks the 30ft rule himself, but with more pleasurable consequences.