Worst episode of the Hartnell era by a long ways. The pacing is plodding, the plot is barely there, and the whole thing is generally tedious. Hartnell's absence is inescapable and you can almost hear Peter Purves' back creak from carrying this story along from game to meaningless game. Given the disastrous behind-the-scenes drama of writing and staging the thing, it's arguably a miracle it's as coherent as it is, but that is extremely faint praise. I am eternally grateful that they didn't end up using this as Hartnell's last story, and that's about the only positive I've got for it.