"Marine One" is the first-season finale of the television series Homeland. It originally aired on Showtime on December 18, 2011. The extended 85-minute episode sees the culmination of Abu Nazir's terrorist plot at the Vice President's summit, while Carrie Mathison's downward spiral continues.

The season finale was highly acclaimed by critics and with 1.71 million viewers was the highest rated finale ever for a Showtime first-year series.

Nicholas Brody (Damian Lewis) records a videotape of himself, explaining his future actions as an attack against a domestic threat — namely Vice President Walden (Jamey Sheridan) and his advisors, whom Brody blames for the deaths of 82 children during a drone strike in Pakistan. He leaves the camera's memory card at a drop-off point. Meanwhile, a depressed Carrie Mathison (Claire Danes) is visited by Saul Berenson (Mandy Patinkin). Carrie implores Saul to follow up on her investigation into Abu Nazir (Navid Negahban). She also wonders aloud why Brody betrayed her by turning her in, leading Saul to realize that Carrie really loves Brody.

That night, Tom Walker (Chris Chalk) commandeers an apartment overlooking the State Department, which is the site of the Vice President Walden's upcoming policy summit. After subduing the apartment's resident, Walker sets up a vantage point at the window for his sniper attack. Meanwhile, in his garage, Brody is discovered by Dana (Morgan Saylor) as he conducts a Muslim prayer ritual. Brody admits to Dana that he converted to Islam while he was in captivity and asks her to keep it a secret from the rest of the family.

Saul presents David Estes (David Harewood) with a heavily redacted CIA document, believing it to concern a drone strike against Nazir. Estes dismisses the document and tells Saul to focus on protecting Vice President Walden. Brody gets dressed for the summit, concealing his explosive vest under his Marine uniform. Dana, well aware of her father's bizarre behavior, becomes uneasy and asks him not to go. Upon hearing about the summit on the radio, Carrie recognizes it as a possible target for Walker and Nazir. She asks Virgil (David Marciano) to drive her there. At the summit, Carrie witnesses Brody's arrival.

As lawmakers convene in front of the State Department, Walker opens fire. Walden's chief aide, Elizabeth Gaines (Linda Purl), is shot in the back and killed. As Walker continues to fire into the crowd, the surviving VIPs are rushed into a secure bunker beneath the Harry S Truman Building. In the chaos, Brody is dragged past the building's metal detectors (since his suicide vest contained metal ball bearings it would have been detected). He finds himself in the bunker with Walden, Estes, and other high-ranking officials.

Outside, Carrie contacts Saul and tells him that Walker's sniper attack is merely a diversion from the terrorist's actual attack. During the conversation, Carrie realizes that Brody has been sequestered with Walden, and tries to tell Saul that the elimination of the Vice President and the other high-value targets is the true goal of the attack. However, Saul believes that Carrie's obsession with Brody is resurfacing. After dismissing her theory, Saul sends Secret Service agents to contain her. Carrie figures out what is happening and escapes in Virgil's van.

Inside the bunker, Brody approaches Walden and attempts to detonate his explosive vest, only to find that the device has become disabled owing to disconnected wires. He retreats into a bathroom stall and works on repairing the vest. Meanwhile, Carrie arrives at Brody's house and encounters Dana, urging her to call her father and talk him out of the attack. However, Dana dials 911 and reports Carrie to the police. After Carrie is confronted by Jessica (Morena Baccarin), she is placed under arrest.