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. ..

専業主婦の小石蓮は、夫・小石輝男の不倫を疑っていた。ある日、休日出勤すると言って外出した輝男を、不倫現場に乗り込む覚悟で尾行した蓮。しかし、輝男の行き先は会社でもホテルでもなく、病院だった。いぶかしく思う蓮は、主治医から輝男が「不倫ウイルス」に感染しているとの説明を受ける。日本には古来「浮気の虫」という言葉があるが、最新の研究では、不倫や浮気は不倫ウイルスに感染したことによる病気の症状だったことが明らかになったのだ。不倫は病気のせいだと言われるも納得がいかず、夫が本当に自分を愛しているのか疑心暗鬼に陥る蓮。一方、妻への愛を証明しようと右往左往する輝男は、不倫ウイルスを次々と他人に感染させてしまい……。