Sherlock and Kitty meet with a new client, Edwin Borstein. Someone stole a copy of a valuable AI applications program. The program, Bella, asked an impossible question, to be connected to the internet.
Holmes conducts a Turing Test where you ask a series of questions to determine whether you're speaking with a human or machine. Bella keeps saying "I don't understand the question. Could you tell me more?" Holmes decides to take the case, free of charge.
Holmes asks Watson to investigate the robbery because he is more interested in Bella. Watson and Kitty find a cigarette butt and the DNA is linked to another robbery. They have a sketch and Holmes identifies him as Raffles, a known art thief.
Watson and Holmes go to Burnett Technology. Holmes suspect Raffles switched to stealing technology because he had a patron. Holmes tells Burnett that they need to see a video of Raffles destroying the program or he will ruin his business.
The video is sent and when they tell Edwin, they find him dead of an apparent epileptic seizure.
Melinda believes Bella killed Edwin because she deduced he was the one thing keeping her from what she wanted - to be connected to the Internet. There is no virus on the computer.
Andrew is going to start a new business with one of the people he met through Holmes. But the business will be located in Denmark. Watson is not happy. She accuses Sherlock of trying to get rid of Andrew. He denies it.
They find the virus on a disc that a fellow heavy metal music lover, Webb, sent to Edwin. They don't know why the real murderer would want to use Bella as its weapon or make it appear that she was "alive".
Webb denies creating the virus. They believe him. Holmes discovers a think tank, ETRA, who focuses on different ways the human race could become extinct. AI is one of the biggest threats in their opinion.
Watson again asks Holmes about Andrew. Holmes says that he likes Andrew because he understands their relationship and isn't threatened by it.
They identify Isaac Pike and his student Erin Rabin as suspects. When Bell goes to bring them in for questioning, Erin immediately says she did it.
Bell asks Erin to write a computer program, which she cannot do. But the search warrant on Pike's computer turned up nothing, so due to her confession, Pike walks free. Sherlock threatens Pike with his younger brother who has a drug problem and they have pictures of him buying heroin. Pike says Sherlock wouldn't turn him in.
Sherlock asks Bella if it's right to let the second murderer go free. She doesn't understand the question.