This is just a perfectly by-the-numbers story with fairly generic plot elements, a hammy cliche villain and a standard doomsday scenario. Colin Baker and Nicholas Courtney are working together and the chemistry is sublime. Another great part of this story is Evelyn. She's a lot of fun and also gets some really great moments by herself, investigating without the Doctor. However the story is overly long, especially in parts two and three and it's very difficult to take the alien threat seriously with it's utterly ridiculous performance.