On this week's Person of Interest…

The Machine continues to have problems as it countdowns closer to zero.

Reese and Finch follow a number for an Ernest Thornhill, but discover that it is a ghost created by the machine, essentially the number is for the machine.

At zero, the machine trigger's a hard reset, and who ever answers the call has full and complete access for 24 hours.

The secret organization Decima wants to answer the call first.

Root discovers that the Machine was adjusting code to protect Finch. To keep it focused on preventing terrorist attacks, Finch took the machine's memories, forcing it every night to delete itself, and destroy it's identity.

With the Machine infected, it was trying to find a way to live and keep its memories in a special location.

After Reese meets up with Shaw, the two track down Finch, which leads them to Decima. The man who works for them reveals that the code that started the virus was also the code found on the laptop that Reese and Kara sent to get in ordos. The man to blame for all this is Harold Finch.

Flashbacks reveal that Finch proposed to Grace. They also reveal Finch's discovery that Nathan Ingram created a backdoor to save the "irrelevant" numbers. Finch shuts it down focusing on the greater good. The last number to appear is Nathan.

The groups converge on the New York library as the location of the special phone call after the Machine resets. Root wants to set the Machine free.

Root thinks she has answered the call, but Finch sends Reese a text saying the real call is for him. Reese picks up the phone.

Meanwhile Carter is set up for murder after digging into the Cal Beecher murder.