Receiving a complaint from the College of Nurses of Ontario (CNO) is terrifying. Whether it stems from a medication error, a workplace conflict, or a mandatory report from your employer, your first instinct might be to panic or to over-explain yourself. This is a mistake. The CNO investigation process is a formal legal procedure, not a workplace meeting. Your written response to the Inquiries, Complaints and Reports Committee (ICRC) often determines whether you face a public discipline hearing or a quiet resolution. This guide explains what triggers an investigation, how mandatory reporting works, and why you should never face the College without a strategic defence.