This episode begins with one of the greatest lines ever in Doctor Who. After the Brigadier steps in and shoots Mailer milliseconds before Mailer was going to shoot The Doctor, The Doctor snaps back at his saviour, "Thank you, Brigadier. But do you think that for once in your life you could arrive before the nick of time?". Brilliant.
I must also mention Michael Sheard's terrific performance as Dr. Summers, a character who always seems to be on the cusp of getting killed off, but constantly finds ways to stay alive and relevant to the story. He even gets an exit scene - an honour rarely bestowed upon minor supporting characters. Summers and Jo have spent a lot of time together during the six episodes, and the way that Summers gently tugs at Jo's chin before he goes off to tend to the wounded in the prison hospital is sweet and touching.
What a fantastic story this is. It contains all the elements of the classic Pertwee era, but in just the right amounts, and never too much at the same time. UNIT is allowed to be UNIT, aided by The Doctor but independent and able to carry out their own plans with varying levels of success. Jo becomes a much stronger character after enduring a great deal during the many prison riots that occur. The Master, as mentioned before, is ultra cool, and is aided by Mailer, one of the best thug performances seen in the series by William Marlowe (Mailer also breaks a taboo on the programme by dropping the first H-bomb ("hell") in Doctor Who history). And, finally, The Doctor gets to be brash, arrogant, caring, jovial, charming, and inventive - all in the same story.
And any concerns that the edge had come off Doctor Who with Terror of the Autons are allayed here when Barnham (and Neil McCarthy's job in bringing him to life should also be commended), a man that doesn't have, literally, an evil thought in his mind, halts his own escape in order to help the fallen Master, and gets brutally run over and killed for his trouble.
Jon Pertwee era Doctor Who has often been compared to James Bond. The Mind of Evil isn't James Bond. It's better.