This story was not completed during its original recording for season 17 of the classic series due to industrial dispute interfering with the schedule. It has since been released as an audio version, as a reconstruction with narration for missing parts, as an audio and animated remake with the 8th Doctor instead of the 4th Doctor and finally this reconstruction with restored original footage and animation for the previously missing portions (which also has an added scene at the end with Tom Baker reappearing as his much older self.) In my opinion this most recent animated reconstruction gives the best depiction of the original story despite limitations with the animation. It allows us to fully appreciate Shada in all its glory.
The story involves the Doctor and Romana arriving at Cambridge in order to see the Doctor's friend and fellow Time Lord Professor Chronotis just as evil scientist Skagra is also looking for him in order to acquire a stolen Gallifreyan book which has the power to release Time Lord criminal Salyavin who has the power to implant his mind into others. Skagra who already has the means to extract people's minds intends using Salyavin's powers for himself.
The adventure is thoroughly absorbing, intelligent and fun. There is very funny humour, quite dark moments and loads of charm throughout. Denis Carey is magnificent as Professor Chronotis, one of the great guest characters both in the idea behind the character and the performance. It is a pity he never appeared again. Other guest characters are all good and Romana is a great companion but above all that is Tom Baker who is at his magical best as the 4th Doctor. He is electrifying to watch and listen to. So funny, so intriguing and so entertaining. This story lets him have a real showcase and that is one of the reasons it is an absolute classic. It is awful that it was not finished and released at the time. Fans were denied this for so long.