Complex sentence: In the depths of Snowcap, Ruby stumbles across a tunnel carved out of the ice itself, and goes exploring--only to find a base where the humans captured from the Torus Antarctica are being dissected and transformed into Cybermen.
Split into simpler sentences: In the depths of Snowcap, Ruby stumbles across a tunnel carved out of the ice itself, and goes exploring. But he finds a base where the humans captured from the Torus Antarctica are being dissected and transformed into Cybermen.