Gu Nian told her about her experience over the past few days. She guessed that the masked man was the Prince of Nanjiang.
Xue Qianyu also told him about what had happened on the North Slope.
When he had received the letter and the bracelet, he immediately thought of the bracelet that he had given to Gu Nian.
There was a very well-hidden and ingenious mechanism on the bangle that only he knew.
Moreover, he had seen it before. Gu Nian had not discovered the mechanism yet, so he had been wearing it. He guessed that the masked man had not found the mechanism either.
Without knowing where the mechanism was, it would be difficult to remove the bracelet from Gu Nian's hand unless you cut off her hand.