In German-speaking markets, the Death Notice trilogy (originally Si Wang Tong Zhi Dan ) is branded as the , referring to the pivotal date (April 18th) of a cold case that haunts the protagonists. The books in the series are:

The incomplete phrase you are referencing is the title of the third book in German-translated thriller series, known as the "Die 18/4-Serie" .

Der Hauptmann und der Mörder: Thriller (Die 18/4-Serie, Band 1)