Root and Finch watch the stock market crash with a group on the street.
The team works their way through the basement to hack the servers and reenable the elevator.
Root and Finch talks to the security guard while posing as repair technicians.
The team heads into the basement server farm at the stock exchange which turns into a Samaritan ambush.
Source: Person of Interest — Wikia
Finch teaches the Machine to play chess in a flashback in the park.