Season: Six — Episode: 21 Director: Christine Moore — Writer: Robert Doherty — Aired: September 17, 2018 — Viewers (millions): 3.10 Summary: Holmes and Watson face their greatest challenge to date when a murder investigation threatens to destroy their partnership.
No. We're much better than that. We're two people that love each other. We always have been.
— Holmes to Watson
In the wake of Michael Rowan's death, Watson is questioned by FBI Agent Mallick. Watson's alibi is weak as she was at her parent's house, but only her mother was present. Mallick believes Watson killed Rowan after he invaded The Brownstone and attacked her as an act of obsession. Mallick plays Watson a recording of Rowan leaving an internet voicemail for William Bazemore when he was killed in which Rowan says "Joan." Watson asks for a lawyer.
The episode title is taken from a famous Conan Doyle Sherlock Holmes quote, "when you have eliminated the impossible, whatever remains, however improbable, must be the truth" which first appeared in The Sign of the Four. Holmes also quotes it in "The Leviathan".