Sherlock enlists Watson's help when a groundbreaking artificial intelligence software program is taken; Joan questions Sherlock's motives after learning that he has been in contact with her boyfriend.
The search for a missing teenager takes an emotional toll on Dodds; DNA evidence could lead to the teen's abductor.
After a female pundit is assaulted during a protest, Benson and Barba struggle to put their political beliefs aside to help bring the attacker to justice.