Complex sentence: Sarah Jane and Luke go through the time fissure again, and discover that present-day London has been destroyed; the Trickster appears to Sarah Jane, and mockingly thanks her for all she's done for him.
Split into simpler sentences: Sarah Jane and Luke go through the time fissure again and discover that present-day London has been destroyed. The Trickster then appears before Sarah Jane and mockingly thanks her for all she's done for him.