Oh I just love this duo of Evelyn and Sixie, they're great together! Part one was fab at setting up the scenario with the Silurians, Darwin and our TARDIS team. That being said, around part 3 I started to feel that it was dragging on a bit, which is the case in most 4 parters for me personally. The themes explored regarding evolution and the origins of the human race are a great aspect to explore, Darwin and the Silurians make for a really interesting combo! That being said, I really wish this didn't fall into the age old trope of the Silurians vs humans which always, always happens. I really do hope there's a non-stereotypical Silurian story out there, somewhere.