Complex sentence: Hiram refuses to take part in the scheme, whereupon Ratigan orders Fidget to capture Olivia so he can feed her to his pet cat, Felicia.
Split into simpler sentences: Hiram refuses to take part in Ratigan's scheme, whereupon Ratigan orders Fidget to capture Olivia. If Hiram refuses to cooperate, Ratigan will have Olivia fed to his pet cat, Felicia.