A culmination of the case for reform, Chapter 8 offers a blueprint for a Universal Partial Defence (UPD), based on an expanded version of the diminished responsibility defence. The proposal actualises the Real Person Approach (RPA) in criminal law doctrine by facilitating consideration of a richer account of rational agency and a wider array of situations that may bear on culpability, in recognition of the vulnerable nature of personhood. In line with the features of the RPA, the UPD expresses conceptual feasibility by relying on bounded causal theory to legitimise the expansion of doctrine, as outlined in Chapter 7. Key requirements of the proposal are explained, and the boundaries of the defence are tested, for example, with an analysis of the potential impact of a cultural defence, and the place of loss of control/provocation-type claims. The chapter concludes with consideration of practical challenges and possible outcomes of a successful defence.