I hate to admit it, but I didn't notice the names before someone on another website mentioned them (there's significance to many more than just Sarah, Helena, Leda and Castor, if you want to look more closely…).

"In London town,
We all fell down,
And Castor woke
From slumber…".

I can't believe this review was so negative when one of the most shocking reveals (at least to me!) finally made sense of much of what they've clearly been building towards for two seasons.