On this week's Person of Interest…

Reese remains behind bars while Carter tries to help get him out. Unfortunately, the FBI deems the suspects as a threat to national security and assigns her as the interrogator.

Finch poses as a substitute teacher to follow a computer whiz named Caleb dealing drugs and dealing with the death of his brother.

Fusco discovers the brothers had been drinking and playing on the train tracks when Caleb's brother died. Caleb blamed himself.

Finch also learns that Caleb has created a compression algorithm which his teacher planned to help sell.

Finch prevents Caleb from killing himself and convinces him to use his smarts and work hard.