Bai immigrated to Singapore and returned to China.

I don't know the details, but generally speaking, if a foreigner violates local laws in Singapore, such as possessing or using illegal drugs, the local police may detain his passport and investigate him. In this case, the person may need to hire a lawyer to help deal with legal problems and solve the matter as soon as possible to return to China.

In addition, if this person is detained for engaging in illegal activities or misconduct, they may face penalties such as fines, detention or deportation. In this case, they need to abide by local legal procedures and contact the local immigration bureau to understand their rights and the next action plan.

Finally, it is suggested that this person's friend contact the local legal aid center or lawyer as soon as possible to get more detailed information and help.