Reese and Finch hurry to help their newest POI, Dr. Richard Nelson, a lauded professor from a local university, but they find that they are too late. Someone has already poisoned Nelson with polonium, a highly radioactive material that, when ingested, eats away at the body from the inside out. Reese knows that Nelson only has 24 hours to live, so he agrees to help the doctor discover who poisoned him and extract vengeance before it's too late. Together, Reese and Nelson go through the clues and eventually discover that he was unknowingly involved in some insider trading, and that trader, Vincent Conrad, wanted to dispose of Nelson to clear up all the loose ends. Reese manages to locate Conrad, allowing Nelson to confront him and give him a taste of his own medicine. Nelson thanks Reese for his help, then passes away. Meanwhile, Fusco finds himself in the middle of a tense Internal Affairs investigation after Detective Azarello decides to rat him out from prison. Fusco denies all the charges, including the charge that he killed and buried Detective Stills, but eventually comes clean to Carter about some of his dirty deeds. Cater is conflicted, but ultimately she winds up helping get Fusco off the hook with Internal Affairs. Finch becomes increasingly more nervous about the machine's effectiveness, given that Dr. Nelson is the third in a series of POIs that they have not been able to save. He wonders what the rapidly approaching deadline for the Stanton Virus could mean for the machine.