While visiting an area near the White HOuse, a father and daughter discover the body of Lt. Commander Edward (Ned) Wallace. His wallet and watch are missing, which leads the NCIS team to first think that he was the victim of a mugging gone wrong.
While examining the scene, Wallace's phone rings. Tony picks it up and discovers the President is on the line.
It turns out Wallace had arranged to discuss something with the President, and was on his way there when he was killed.
A U.S. Park Police Sergeant said told Gibbs there had been a number of recent muggings in the area.
The NCIS team discovers the mugger - a man, by the name of Nicholas Dunne - but determines he hadn't killed anyone. He had been using a rubber knife to do his robberies.
Tony and Bishop visit the dead lieutenant's yacht, and discover evidence of another woman there. Plus, it turns out the lieutenant had been getting ready to divorce his wife.
They discover that the other woman is Courtney Reed, a former Navy Lieutenant.
They track Reed to a motel, where she's been living under a false name. When Tony and McGee go to get her, she tries to escape them.
It turns out that Reed had been working for a security firm, and had discovered a security breach in their firewall which would allow hackers to infiltrate their files. Upon informing her management, they told her not to say anything - they were worried about bad publicity.
When she told her lover - the now-dead lieutenant - he told her to hide. Afterward, someone had run her off of the road, trying to kill her.
In the meantime, the lieutenant had tried to see the President to tell him what was going on - only he was killed before he could do so.
Gibbs arrested, the company officer - named Bryce Tolson.
While all of this was going on, Vance had gotten some worrisome news - it looked as though there may have been cancerous spots on his lungs. After going in for a biopsy, it turn out to be benign - a virus which mimics the look of cancerous spots was the culprit.