Ren Koishi, a housewife, suspects her husband, Teruo Koishi, of having an affair. One day, Ren follows Teruo when he goes out for work on his day off, determined to get to the scene of the affair. However, Teruo's destination was neither a company nor a hotel, but a hospital. Ren, who is suspicious, receives an explanation from his doctor that Teruo is infected with the 'adultery virus'. In Japan, there is an ancient term 'cheating bug', but the latest research has revealed that adultery and cheating were symptoms of a disease caused by infection with the adultery virus. Ren is unconvinced that his infidelity is caused by the disease and is doubtful whether her husband really loves her. Meanwhile, Teruo, who is trying to prove his love for his wife left and right, infects others one after another with the adultery virus. ..