I think it would be fair to say that based on Planet of Giants and Day of the Daleks that Louis Marks is not the show's finest writing talent, however I feel that under this mid-seventies production team he produced his best work with Planet of Evil. The story in the most part is reframes the core concepts behind the characters of Jekyll and Hyde, this can be seen in both the planet The Doctor and Sarah Jane land on and the scientist character Sorenson. The planet has something Sorenson wants, he takes it and then the planet wants it back.

This simple, effective story (thank God it's not stretched over six episodes!) is elevated considerably by the outstanding design work seen throughout the production, most production teams would have produced the same script to inferior effect. The planet looks as real as could be conceived with the budget they had and outstrips anything seen on Doctor Who up until this point. The sets and props are detailed and fully thought through, they build a believable world. By this I'm not just referring to the outstanding alien jungles, but also the machinery, weapons and living areas which have the most incredible attention to detail.

Tom and Elizabeth look ridiculously comfortable in the role as do the wider guest cast. David Maloney delivered some very talented direction making best use of the impressive sets and talented actors. The lighting in this era of the show continues to be brooding and moody - delightful!

This is all I have to say. Average script, amazing production, direction and cast.