Impermanence

A childhood friend who had been missing for two years suddenly returns, but his personality has completely changed. He not only mocks Gu Changjun, but sometimes acts as though he doesn't even know him. Gu Changjun is completely baffled. Still, he decides to protect Wen Zichang, just as Wen used to protect him before he disappeared. And he is determined to find out why Wen Zichang became this way!

After Gu Changjun shamelessly sticks by Wen Zichang for a while, he begins to suspect that Wen may have stumbled into a cold case even he would find hard to solve. Then, after accidentally discovering one of Wen Zichang's secrets, Gu Changjun becomes even more desperate to learn what happened during the two years Wen was missing.

This is a serious story with a romance, but the relationship isn't the main plot, so it doesn't really count as a romance novel. The mystery is the main plot.

Thanks in advance to everyone who gives this a read! You can also try solving the mystery yourself! This is my first mystery novel, so please let me know if there's anything I can improve!