In the archives of the as-yet non-digitized collections of the International Tracing Service (ITS) in Bad Arolsen there is a copy of Alan Burgess’s 1950 BBC radio play, The Greatest Detective Story in History. The play, which presents a moving and insightful analysis of the work of the ITS, reveals how much was known about the crimes of the Nazis so soon after the war. This article uses Burgess’s play in order to focus on the operation of ITS’s child search branch. It shows how Burgess’ play was based on detailed knowledge of the problems encountered by the field workers in their search for non-German children. The article then goes on to consider why the work of ITS was deemed an appropriate topic for a radio drama in Britain in 1950 and to argue that, with respect to the development of British memory of Nazi crimes, Burgess’s play perfectly captures the ways in which the Third Reich was understood in Britain in the postwar years: as a vast act of criminality which the British could proudly claim to have helped to destroy. At the same time, from today’s perspective, one can see the limits of its analysis: the play was circumscribed by culturally-familiar narrative frameworks and conventions; its gender politics were markedly old-fashioned; and its reluctance explicitly to identify specific victim groups (such as Jews and Polish Gentiles) suggests a degree of confusion over Nazi “population policies”. Nevertheless, the play also reminds us of the postwar moment when Britain was proud to be involved in international organizations and when rebuilding Europe was felt to be in British interests.