This article explores the humanitarian principles of universality, impartiality, and neutrality, and the moral boundaries of humanitarian action in the past. It does so through a case study of the International Committee of the Red Cross (ICRC) and Kenya’s Mau Mau rebellion (1952-60). Drawing on the vocabulary of denial, and on the spaces in which something is both ‘known’ and ‘not-known’, it asks why the ICRC were reluctant to respond to allegations of torture in Kenya’s detention camps and prisons, and explores reasons for its later positive assessment of detention conditions. The article advances two arguments about the ICRC and Mau Mau. Firstly, that ideas about race and cultural difference helped provide a moral justification for the avoidance of politically-sensitive decisions about Kenya and may have fed into the down-playing of evidence of abuse. Secondly, that the ICRC became entangled in the British Government’s project of denial. By drawing on the language of detention and interrogation developed by the British, the ICRC fed into and confirmed an official version of events. In doing so, the article reveals the uneasy relationship between key humanitarian principles and denial, and highlights how the impartiality of classical humanitarian actors like the ICRC could be invoked by powers committing abuses and cover-ups.