Grandma Ye Shurou from Chaoshan lived a simple life, enjoying her twilight years. Her grandson, Xiaowei, burdened by debt, secretly traveled to Thailand to find his rumored billionaire grandfather, Zheng Musheng. However, Xiaowei returned with shocking news: his grandfather was long gone, and the person with whom Grandma had exchanged love letters was a complete stranger. As Xiaowei investigated, a love affair hidden for half a century suddenly surfaced, striking Grandma's heart.

龙番市刑警队长林涛（李现 饰），与法医科科长秦明（张若昀 饰）是多年的老朋友。秦明的助理因不堪忍受秦明的古怪脾气打报告辞职。痕检科的李大宝（焦俊艳 饰）被借调加入工作小组。期初秦明对身为女生的大宝不信任，但倔强的大宝在破案中，体现出了相当不错的推理和观察能力，并且嗅觉极度灵敏，挑剔的秦明决定留下大宝。龙番警局的铁三角也初告形成。他们互相合作，接连破获了各种匪夷所思的案件。 本剧改编自秦明悬疑推理小说《第十一根手指》。