As the medicalization of criminal behaviour expands through forensic psychiatric practice it is reliant upon a therapeutic ideology based on clinical assessment and effective application of treatment strategies. When such criminal offenses are particularly heinous the perpetrators are often referred to as evil by non-professional accounts. However, the extent to which the concept of evil affects the perceptions of mental health professionals working with such offenders is little understood. This paper reports on research conducted in a high-security psychiatric hospital in the North-west of England and examines the construction of care plans in relation to a number of mentally disordered offenders who are considered by a group of mental health professionals as evil. Thematic analysis of mental health professionals' discourse pertaining to the care plans revealed a complex motivational and rational structuring of evil that dictated the switch from medical ideological discourse to lay notions of badness. From this, an Airaksinen model was constructed to display the types of evil manifestations.