Complete story — includes the ending
Mathematician Felix Soto is murdered. His walls are covered in invisible ink with his work, which is about the P versus NP problem, one that has bedeviled mathematicians. Soto's research partner Cyril Nauer is also murdered, and a mugger was shot and left for dead after seeing the killer leave Soto's apartment. The proof that P equals NP would be worth millions. Professor Tanya Barrett evaluated Soto's work and said that they were not near a solution. Sherlock deducts that Barrett solved the problem herself, but needed more time to cash in on it. Barrett is arrested, but the federal government takes over in the interest of national security. Meanwhile, Joan meets with the son of the patient she lost during surgery; she gave up her medical career after that death. The son asks her for money to invest in a bar. She previously bought him a car, and Sherlock thinks that the young man is using Joan's guilt to extract money from her. Sherlock offers her $22,000 to buy him out of her life. She offers it as monetary support only for the son's education, but he reacts coldly to the offer.
Sources and content license
Source and revision history · Adapted from Wikipedia contributors, List of Elementary episodes. HTML formatting and reference markers removed. · Content license