On this episode of Person of Interest…

Finch heads to the NSA to unleash the Ice 9 virus to destroy Samaritan.

The virus, which is only activated with Finch’s voice, would also destroy the Machine.

The Machine sends Reese and Shaw on a mission to track down Greer, which leads them to Finch.

Greer attempts to sacrifice himself and kill Finch, thus saving Samaritan.

Reese and Shaw with the Machine’s help rescue Finch.

Reese and Shaw get to safety as Finch heads to activate the virus.

Despite Samaritan’s protests, he does.

Finch is also shown an alternate world if the Machine didn’t exist, including Nathan being alive but Finch never meeting Grace, Shaw continuing her work with the government, Reese saving Jessica but her pushing him away and leading to his death, Carter getting a promotion and Fusco ousted, Root working with Greer, and Samaritan still existing.

Fusco also is almost killed, but he manages to survive and turn the tables on the agent.