the onus-like all other exceptions in Chapter IV of P.P.C. will be on the defence (accused) to prove such a plea as contemplated in Article 121 of the Qanun-eShahadat Order, 1984 (QSO). As per Article 121 of QSO, the onus is on the accused to prove that when the alleged act was committed, he/she was suffering from a mental illness which made him/her incapable of knowing the nature of the act or that what he/she was doing was either wrong or contrary to law. While considering the case law referred to herein above, we hold that in the case of a special plea under section 84, P.P.C., the Courts should keep the following principles in view:(i) It is the basic duty of the prosecution to prove its case against the accused beyond reasonable doubt and the prosecution will not be absolved of this duty if the accused is unsuccessful in proving a plea raised on his/her behalf. (ii) Where the accused raises any specific plea, permissible under the law, including a plea under section 84, P.P.C., the onus to prove such plea is on the accused. However, while proving such plea, the accused may get benefit from any material, oral or documentary, produced/relied upon by the prosecution. 44. Now we address the second question, "How should the trial Court deal with the claim that due to mental illness, an accused is incapable of making his/her defence?". To answer this question, reference to the relevant provisions of Cr.P.C. is essential which are being reproduced:464. Procedure in case of accused being lunatic. (1) When a Magistrate holding an inquiry or a trial has reason to believe that the accused is of unsound mind and consequently incapable of making his defence, the Magistrate shall inquire into the fact of such unsoundness, and shall cause such person to be examined by the Civil Surgeon of the district or such other medical officer as the Provincial Government, directs and thereupon shall examine such Surgeon or other officer as a witness, and shall reduce the examination to writing. (1A) Pending such examination and inquiry, the Magistrate may deal with the accused in accordance with the provisions of section 466. (2) If such Magistrate is of opinion that the accused is of unsound mind and consequently incapable of making his defence he shall record a finding, to that effect and, shall postpone further proceedings in the case. 465. Procedure in case of person sent for trial before Court of Session or High Court being lunatic. (1) If any person before a Court of Session or High Court appears to the Court at his trial to be of unsound mind and consequently incapable of making his defence, the Court shall, in the first instance, try the fact of such unsoundness and incapacity, and if the Court is