When you watch Elementary Season 4 Episode 21 online, Joan continues her surreptitious digging into Morland Holmes's actions in regards to the Russian hitman through her blackmail of the mole in Morland's company. Emil Katz is afraid for his life, but Joan demands he continues looking into the matter, lest she reveal to Morland that he'd been a mole all along. But will Morland discover the truth anyway without her help? And what will happen if he does? She and Sherlock are then called to a strange case of a double-homicide. Their trained eyes quickly observe that the scene is oddly staged, and later figure out that not only was the scene staged, the two victims were attempting to stage a fake murder when they were both killed for real by a third, unknown, person. What could have happened to lead to this odd chain of events? And does it have anything to do with a worthless property up near Lake Placid? It's a case of murder and blackmail, revenge and jealousy as Sherlock, Joan, Marcus, and Gregson try to figure out the truth. Find out the truth for yourselves when you watch Elementary Season 4 Episode 21 online, right here at TV Fanatic!