In 2035, with the increasing demand of human survival resources, the earth is exploited vigorously, which directly or indirectly leads to the birth of ecological diseases, and the patients may relapse even after being cured. Therefore, for the continuation of human society, all people who have been cured of ecological diseases should make an indelible mark on the back of their hands, in case they relapse at any time and lead to a larger scale of infection. They are called The Lurker. Fiction writer Teng is one of them. Teng met a girl called Ling Yan in the coffee shop he often goes to, and she is not a The Lurker. The two hit it off and quickly fell in love. It was not until Teng heard the news that Mr. Li in the coffee shop died because of a recurrence of ecological disease that he realized the huge impact of The Lurker identity brought to him.