There is a clear rationale for developing interventions targeting negative symptoms of schizophrenia as these are a stronger indicator of current and future functioning than positive symptoms and because they respond poorly to medication and existing psychological interventions. This is reflected in the NIMH-MATRICS consensus statement that emphasised that persistent negative symptoms represent an unmet therapeutic need for patients suffering from schizophrenia. The purpose of this study is to evaluate, in a scientific manner, the intervention developed by Swanson et al. 2021: Metacognitive Training (MCT) Minus. The MCT was adapted to target negative symptoms in psychotic disorders (e.g. schizophrenia, schizoaffective or non-affective functional psychosis) as the original version of the intervention focused exclusively on positive symptoms. The specific aim is to study whether MCT Minus is a promising treatment for the intended population in terms of reductions in negative symptoms, severity of defeatist attitudes, internalised stigma, and depression as well as improvements in reflective ability and overall functioning. The research will add to existing research by identifying and measuring potential mechanisms of change for negative symptoms (i.e., defeatist attitudes, reflective functioning, stigma and depression). It will also add to the existing evidence base by measuring whether the cognitive biases addressed in MCT lead to changes in the wider conceptualisation of metacognition used elsewhere and whether the promising results seen in the feasibility study of MCT Minus can be replicated in a randomised controlled trial (RCT) with a control group and a blinded assessor. The researchers also hope to replicate the findings of a previous study, where MCT was found to be related to the modulation of default-mode network (DMN) homogeneity in schizophrenia, an area thought to be involved in self- and other-reflectivity.