In Episode 11 ("Down Where the Dead Delight") , a bomb detonates in a morgue, forcing Holmes and Watson to solve a murder without any physical "pieces" of evidence.
In this episode, Sherlock Holmes and Joan Watson investigate the murder of a young woman. Their investigation reveals that her death is directly linked to a that has ties to a crime committed years prior. The case involves: Elementary - Season 4
Season 4 heavily focuses on Sherlock’s estranged father, Morland Holmes (played by John Noble), who arrives in New York to "fix" his son’s life. His presence is a major missing piece of Sherlock's backstory that is finally explored. In Episode 11 ("Down Where the Dead Delight")
The "piece" in question leads the duo into the world of high-stakes art, where they must determine if the victim was killed because of what the artwork represented or a secret it contained. The case involves: Season 4 heavily focuses on