Sherlock returns to New York with a new apprentice and a renewed interest in working with the NYPD after being fired by London’s MI6. However, Gregson won’t let him resume consulting for the department without permission from his former partner, Joan, the NYPD’s new go-to private investigator.

Sherlock helps a math genius from his network of 'Irregulars' experts after he stumbles upon a body while participating in a math puzzle competition. Joan attempts to extend an olive branch after she learns about Kitty’s past.

Sherlock takes on the case of a stolen artificial intelligence software program, but seeks out Joan when he'd rather disprove the computer's abilities than find the thief. Joan meets Sherlock head-on when she finds out he's met with Andrew without telling her.

When a debt collector is murdered, Holmes and Watson try to narrow down the suspect pool from thousands of consumers who owed the victim money. Meanwhile, Watson’s relationship with Andrew progresses when he asks her to meet his father for the first time.