Stan pursues a lead that puts him on the trail to one of Gregory's crew members; when Gregory is compromised, the KGB offers to bring him to Moscow.
With the arms control summit under way, a shocking revelation from Philip throws Elizabeth and her work into turmoil; Stan follows a dangerous hunch.
Frank goes on high alert when a threat to NYC may be imminent following a terrorist attack in the Middle East.
A teenager (Astro) whose brother was recently murdered is identified as the latest person of interest; Finch fears that his ex-partner's son is getting close to discovering the machine.