This is a heavy book with which to make a leap of faith: to trust that one life can make a difference in the deeply compromised pursuit of international justice and security. In the epilogue to her biography of Sergio Vieira de Mello, Samantha Power suggests ‘if there was anyone who could have wrung from the UN whatever reform and promise it could muster, it was he’. In this long book, depicting some of the worst that humanity can inflict on itself, Power builds this image of Vieira de Mello. If her claim for his significance is justified, then we might indeed revisit the conditions for such faith.