|Doctor Who-The Trial Of A Time Lord|
The doctor finds his TARDIS whisked out of time for him to stand trial before the time lords. The prosecution is someone addressing themselves as the Valeyard. And from the beginning all of his evidence against the doctor is entirely circumstantial. In his first piece of evidence the doctor and Peri are on Ravalox,which turns out to be Earth after a cosmic shift which rendered it nearly uninhabitable and vulnerable to con artists such as Sadalom Glitz,who makes his debut on the series in this episode. With the time lords still not quite convinced ,another story is presented where on Thoros Beta the doctor seems to ally himself with his enemy Sil whose using the planets population for biological experimentation. The doctor is lead to believe this resulted in the death of his companion Peri.
It is learned through his own revelation that the Valeyard is actually something of the doctors skin of evil created in between his final two incarnations who wishes to see his good side admit the evil within him. The most damaging evidence is yet to come as the doctor and new companion Mel is depicted in some future time on a 30'th century Earth passenger liner where the peace is being shattered by mad scientists creating a human/plant hybrid who have the potential to cause the extinction of humanity. The doctors destruction of this hybrid race is seemed to be grounds for removal of his remaining regenerations. At this point another old adversary The Master is revealed to be a part of the scheme with the Valeyard. After going through a huge elaborate deception within the time vortex itself,the doctor (with the help of Mel's testifying and Sabalom Glitz's assistance) manages to defeat the Valeyard and return on his missions in the TARDIS with Mel in tow.
Each of the stories in these series presents extremely complicated scenarios. Especially when the doctor learns that for all intents and purposes it is himself whose acting as his own prosecution. The doctors behaviors involving both Peri,who the timelords claim was actually married off rather than killed on Thoros Beta as well as his actions on the space liner do in fact indicate the sort of callous behavior that might've led to the creation of the villainous Valeyard sometime later. This was probably a reflection by the serial's writers and producers that Colin Baker's portrayal of the doctor represented some of the characters darker traits. It's also perhaps hinted here that those darker elements of the Valeyard might've been responsible for the sixth doctor's difficult and unstable personality all along. So while opening a new door for the show,as well as being an exit point for companion Peri and an entrance for new companion Mel,played by Bonnie Langford this would be the end for Colin Baker on the show. He was fired shortly after this production,the only doctor ever to have this done to them. So without any hesitation,a new actor to play the seventh doctor would have to be chosen.