Complex sentence: Dresden is captured by Bianca and locked in a room with Justine and Susan, who has been partially turned into a vampire, a process that will be completed if she kills a human through vampiric feeding.
Split into simpler sentences: Dresden is captured by Bianca and locked in a room with Justine and Susan. Susan has been partially turned into a vampire, a process that will be completed if she kills a human through vampiric feeding.