It is essential that a defendant's fitness to plead be accurately assessed in order to ensure that those who are unable to effectively participate in their trial are not required to do so. With a mandate from the Law Commission, a new measure, the 'FTP' has been developed; this measure is designed to assess fitness to plead in terms of the defendant's decision-making capacity. What has not been determined to date is whether this new measure is vulnerable to attempts at malingering. The current study is an investigation of the FTP's effectiveness in detecting malingering, as well as an exploration of the sample's understanding of fitness to plead and how this could potentially be malingered. This study employed a between-subjects, double-blind, mixed-methods design, involving two groups: simulated malingerers group and a control group. Sixty-four students were recruited to this study, primarily via a research credit participation scheme. All participants completed the FTP measure and the Ravens Standard Progressive Matrices (RSPM). The RSPM was used as a criterion measure of malingering. Participants also answered qualitative questions regarding their understanding of fitness to plead and their simulated profile of unfitness. Results indicated that the FTP's malingering items were not sensitive to attempts at malingering; Content Analysis revealed that participants primarily indicated mental health problems, and to a lesser extent, cognitive difficulties as the reasons someone would be found unfit to plead; the most commonly attempted means of malingering was that of malingered cognitive impairment. Recommendations are offered to assist clinicians in detecting malingering while using the FTP, and the clinical and theoretical implications of the current study's results are described.