In the Season Four finale, Finch and Root race to save The Machine, which has been located by its AI rival, Samaritan. Also, Reese is caught in the middle of the final showdown between rival crime bosses Elias and Dominic.
Danny consults a psychic to solve the murder of a young boy; Frank is at odds with the mayor over how best to protect the city from an uptick in crime following a high-profile shooting; Erin investigates a decades-old case.
After a member of the inner circle of a terrorist organization falls ill with a deadly virus, Elizabeth attempts to use his weakness to secure the release of a group of schoolgirls that are being held captive.