From Heroes Wiki
Linderman's tape is a recording of a surveillance tape, burned to DVD. It contains a recording of a tryst between Jessica Sanders and Nathan Petrelli at the Montecito Casino.
When Niki Sanders refuses to go through with the plan to seduce Nathan Petrelli, Jessica takes over and finishes the job. The security cameras at the Montecito record the action.
Niki wakes up alone in Nathan's Montecito hotel room. His campaign manager blames her for Nathan's absence, but Miss Sakamoto arrives and defends her.
Sakamoto shows Niki a clip from the tape when Niki believes that she did not go through with the plan to seduce Nathan. Later, Nathan and Sakamoto discuss the tape. She tells him it's a favor for which he will repay Mr. Linderman later.
A DC reporter shows the DVD to Tracy Strauss, who looks exactly like the woman on the tape.
Tracy shows Nathan the recording of her doppelgänger.