At first, when Qinghe was not in the villa, they didn't take it too seriously, as it was common for any of them to disappear for a day or two. However, they grew concerned when Qinghe left for some errand without informing anyone and didn't return, especially since they now considered each other friends and it was natural to inform each other about their whereabouts.
Eventually, they sensed that something was amiss. Zuo Zhizhen thought for a while and suggested fetching the surveillance tapes. The students at the school were quite pampered, and for the sake of both the students and the school, surveillance was nearly omnipresent.
When Zuo Zhizhen proposed this, they realized the severity of the situation. Although Zuo Zhizhen was taciturn, his words carried the most weight among them, and his thoughts were mature and steady.
