Complex sentence: Gilbert starts to sense that something nefarious is afoot and suspects that the gregarious Mifflin is involved in a plot to kidnap Titania, and he assigns himself the job of protecting her.
Split into simpler sentences: Gilbert starts to sense that something nefarious is afoot. He suspects that the gregarious Mifflin is involved in a plot to kidnap Titania, and he assigns himself the job of protecting her.