In Lonesome Road, the Courier is contacted by a man named Ulysses, who refused to deliver the Platinum Chip at the beginning of the main game. Initially, Lonesome Road was planned to be released in August 2011; however, the DLC was delayed for unspecified reasons, with senior producer Jason Bergman stating "This isn't due to any major issue with the code or content, but there are lots of factors involved in releasing these things, and one of those is causing us to slip past our intended release date." Bethesda were unable to provide a new release date for the DLC, but did state that it would be released as soon as possible. On August 25, 2011, Bethesda announced that the DLC will be released on September 20, 2011. Lonesome Road will conclude the story of the Courier, the main character of Fallout: New Vegas.
Lonesome Road focuses on Ulysses, a former Frumentarii of Caesar who had discovered the "Divide": a glorious land until the New California Republic annexed it. This caused Caesar to retaliate and send a small army to seize the Divide, resulting in the NCR ordering the Courier to deliver a package which would trap the armies of the NCR and the Legion and turn the Divide into a tornado strewn land full of ghouls, called Marked Men, and other dangers. Ulysses believes the Courier to be responsible for the mess of the Divide and when he is ordered to deliver the Platinum Chip, he realizes Benny's plan and discovers the Courier to be alive. When discovering the Courier isn't dead, Ulysses contacts the Courier and asks him to enter the Divide, evoking the start of Lonesome Road.
Source: Wikipedia, "Fallout: New Vegas", available under the CC-BY-SA License.