Submitted by DMoore

Ygor (Bela Lugosi) recovers the weakened Monster (Lon Chaney, Jr) and they make their way across Europe to find Dr. Frankenstein’s other son, Ludwig (Cedric Hardwicke). 

Ludwig decides to transplant the brain of kindly (but murdered) Dr. Kettering into the skull of the Monster but is betrayed by Ygor and Ludwig’s assistant Bohmer, who secretly replaces Kettering’s brain with Ygor’s. 

As the insane Ygor-Monster declares world domination, sudden blindness strikes. The sightless monster panics, his rampage setting the lab afire and he presumably perishes.