Perhaps the most disappointing Sontaran tale to-date, this double header just doesn't cut the mustard. There are moments of genius contained within the story but the pace is too slow and there's too much filler. This could have made for a great single episode but I'm not truly impressed with the quality of Helen Raynor's script.
While the effects work continues to impress, the quality of this adventure is not up to previous installments. I'm complained about the scope of recent "Who" stories before and this is no exception. In "The Poison Sky" the whole planet is at risk. Whatever happened to good old fashioned "domestic" peril? Tennant and Tate continue to be a classic double act while Martha seems a little out of her depth. The next episode should prove a very interesting one...
8 out of 10.