What was Watson hiding?
That was revealed on Elementary Season 6 Episode 4 when she and Holmes worked on a case involving the murder of her former psychologist.
This secret prompted Watson to make a life-changing decision, and it shocked Sherlock to the core as he tried to process the revelation along with his ill-health.
The duo also had to contend with the possibility that someone close to them was not who they thought they were.
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Paul Dailly is a staff writer for TV Fanatic. Follow him on Twitter.