The Tell Tale Tooth - S1.E17

When a massive diamond -- The Cyclops' Eye -- is brought to town for an exhibition, Harris is in charge of a security team protecting the diamond case, which can only be opened using a combination of three keys. Harris gives one to the Police Chief for safekeeping, one to Commandant Lassard, and keeps the third himself. But the Magnificent Mystopholes hypnotises Hightower under the pretense of curing his fear of dentists, while actually using him to steal the three keys to unlock the Cyclops' Eye diamond case, aiding his twisted plot of mass hypnosis.