The Investigation of Lucy Letby offers a clear and structured examination of one of the most complex criminal cases in modern British history. Drawing on publicly available records, court proceedings, and credible reporting, this book explores how a series of unexplained incidents in a neonatal unit led to a major criminal investigation, a high-profile trial, and far-reaching questions about healthcare oversight. The book follows the case from its earliest warning signs through the police investigation, courtroom proceedings, and the wider aftermath. It examines how evidence was gathered and presented, how the legal process unfolded, and how institutions responded before and after the verdicts. Beyond the individual case, it also addresses systemic issues within healthcare settings, including accountability, reporting failures, and patient safety. Written in a factual and measured tone, this work avoids sensationalism and focuses on understanding the investigation, the judicial process, and the lessons that emerged. It is intended for readers interested in true crime, criminal justice, healthcare ethics, and institutional responsibility. This book serves as a comprehensive case study of the investigation, its impact, and the questions it continues to raise.