Perhaps I am in the minority here, but I loathed this episode. The story of the Eternals was gorgeous and the historical setting was beautiful, but that's where it stops for me. Nothing else about this one worked for me. I hated the pacing, and the way that the characters bumble along without much happening. The Eternals were pointless and not nearly as menacing as they should have been, and I spent the entire episode waiting for the punch that I felt sure must have been coming. And then it didn't.

Instead of this, what you want to watch is Sarah Jane Adventures: The Nightmare Man. That's this concept done properly.