[s2e2] The Hounds Of Baskerville < Free Access >

Sherlock realizes the drug isn't in the sugar or the water—it’s in the of Dewer's Hollow.

That night, Sherlock and Henry venture into Dewer’s Hollow. In the darkness, amidst the swirling mist, they see it: a massive, snarling beast with glowing eyes. The Great Detective’s Doubt [S2E2] The Hounds of Baskerville

As the fog rolls in, Frankland appears. He has leaked the gas again to finish Henry off. In the chaos, a common stray dog (enhanced by the gas to look like a monster) is shot by John and Lestrade. Frankland flees but wanders into a Baskerville minefield, meeting a fiery end. The Aftermath Sherlock realizes the drug isn't in the sugar

The investigation centers on , a top-secret military research base nearby. Rumors of genetic mutations and "super-dogs" swirl among the locals. Using Mycroft’s high-level security clearance (stolen, of course), Sherlock and John infiltrate the facility. They encounter Dr. Stapleton , a geneticist with a missing glowing rabbit, and Dr. Frankland , a friendly scientist who was a close friend of Henry’s father. The Great Detective’s Doubt As the fog rolls

They rush back to the Hollow to find Henry on the verge of suicide, driven mad by the gas. Sherlock explains the truth: Henry didn't see a monster twenty years ago; he saw in a gas mask and a "H.O.U.N.D." t-shirt, murdering Henry's father over the secret of the gas. Henry’s child-mind interpreted the mask and the red goggles as a demon dog.

Back at the inn, the unthinkable happens. Sherlock Holmes—the man of pure logic—is trembling. He confesses to John that he saw the hound. For the first time, Sherlock cannot trust his own senses. This doubt leads to a breakdown of his "Mind Palace," nearly destroying his friendship with John as he lashes out in fear.