Arrival is the 22nd episode, season finale of Season One and the 22nd produced episode of The Event. With the cancelation of the series by NBC this is likely the series finale leaving a lot of unanswered questions.
Blake Sterling contacts Elias Martinez and Richard Peel to inform them about Sophia's planned release of the virus, but they can only send armed forces to the two secondary targets, while shutting down the Dulles Airport would require order from the Acting President Raymond Jarvis. Martinez confronts Jarvis, but cannot convince him that Sophia would release the virus on US soil. Despite fainting just before a first attempt to be reinstated by the Cabinet, Martinez then discredits Jarvis with a recording from their previous conversation.
Sterling, Simon Lee, Sean Walker and Vicky Roberts rush to Dulles to stop the virus being spread. Sterling and Simon track down the pilot smuggling the virus canisters into the restricted areas of the airport, but he escapes after wounding Simon. The pilot meets with Sophia and Carlos Geller, but they are attacked Vicky, who shoots the pilot. Sophia flees with one canister, and Carlos attempts to open the other, but is killed by Sterling.
Sean follows Sophia, who locks herself in an empty bureau. Sean argues with her, telling her of the failed other releases and the lockdown of the airport, meaning she would only murder all humans in the airport, but achieve nothing else. Troubled, she ultimately surrenders.
Before heading back to the White House, Simon tells Sean that his people are from Earth, but that they left to prevent The Event, which they feared to destroy humanity, and that all answers would be in the scrolls that Dempsey gave him. In the president's office, Simon states that the portal process will not be stopped, even without the virus "making room" on Earth.
Sean visits Leila in a hospital, and she tells him she is pregnant.
As the earthquakes get stronger, Sophia is brought to the White House, and she claims the spread of the virus to be an "act of mercy", as her people would still need to "make room".
The portal activates fully, and transports the alien planet into the solar system, its southern half apparently ravaged by volcanoes.