"An Invisible Thread" is the twenty-fifth and final episode of the third season of the NBC science fiction drama series Heroes and fifty-ninth episode overall. The episode aired on April 27, 2009. It marked the end of the Fugitives volume, as well as its 2008-2009 season run. It ended with a brief introduction to the next volume, entitled Redemption.
Beginning from where the previous episode ended, Sylar is shown to be unaffected after Emile Danko attempted to incapacitate him by stabbing Sylar in the back of the head. Sylar explains that by using his shape-shifting abilities, he has moved the weak spot. Sylar then morphs into Danko and kills an agent, framing Danko for the murder. Sylar morphs into an agent and helps apprehend the furious Danko.
Meanwhile, it is revealed that when Noah Bennet and his car had been stopped at the roadblock, Claire Bennet and Angela Petrelli were not actually in the vehicle. A little while previously, Noah had realized the construction crew roadblock was a set-up, and had Claire and Angela leave the car, resulting in only Noah's capture. From there, Claire and Angela head to the Capitol building in Washington, D.C., where Angela tells Claire to find her father, Nathan Petrelli. Angela says she has dreamed the future, and leaves to go find Matt Parkman, explaining Nathan will be in trouble and Matt will be able to save him. Claire meets Nathan in his office, though actually Sylar in disguise, and wishes to accompany him to warn the President about Sylar. Sylar agrees, though he intends to meet the President so he can become him. The two go to meet the President, but are instead directed to a suite to wait for him. Claire notices that Sylar, as Nathan, uses the wrong hand to sign his name at the required sign-in checkpoint and deduces who he really is. Sylar holds her hostage and begins to toy with the possibility of her becoming his First Lady.
Following his nosebleed from the previous episode, Hiro Nakamura is able to stop time and he and Ando Masahashi break into Building 26. Hiro and Ando find the prisoners hooked up to the drugs and replace them with members of the Building 26 unit. When Hiro reverts time, he begins to feel dizzy again and starts to bleed from his ear. Also freed from among the prisoners, Mohinder Suresh informs Hiro that his body is rejecting his power, and stopping time again could result in his death. Also in the building, Danko and Noah are being held in a room, though Hiro had opened the door when he had stopped time. Danko proposes they work together to take down Sylar, intending to use a tranquilizer to subdue him. However, Danko turns to use it on Noah, but Hiro stops time once more to take the tranquilizer from him and injects Danko with it. Hiro reverts time and then collapses, while Noah calls Claire to check up on her. Noah is stunned to hear Sylar answering her cell.
Having followed Nathan, Peter Petrelli finds the now conscious Nathan, and the two head to find Sylar and Claire. They reach the room where Sylar and Claire are, just as she is thrown out of the room. Nathan and Peter fly in and have a brief duel with Sylar, resulting in Sylar and Nathan flying off. Claire rushes in only to find Peter, who confirms he has taken Sylar's power and they can now stop Sylar. The two head downstairs to meet Noah. Meanwhile, Nathan crash lands into the previous room, followed by Sylar who slits Nathan's throat, killing him. Disguised as Nathan, then as Chief Aid, Sylar is able to meet up with the President. He enters the President's limo and takes the president's extended hand. In doing so, Sylar reverts to his original form and is injected with the tranquilizer by Peter, who absorbed Sylar's shape-shifting ability to take on the President's appearance.
Angela manages to find Matt stepping off from a bus, who was intending to head to Building 26 to stop the agency. Angela convinces him to come with her, and they head to the room where Nathan was. Angela is thus horrified to find Nathan's body in the room. Noah then brings up the body of the unconscious Sylar, explaining they intend to use Matt to mentally alter Sylar's mind to believe he is Nathan, with Sylar's acquired ability of reading the history of objects enabling him to fill in the gaps of Nathan's life, and fully embody Nathan's personality and gain his memories. Initially Matt is reluctant, but Noah convinces him that Nathan would be the only person that could convince the President to shut down Building 26 or any such future agency. Matt finally agrees and does so, causing Sylar to forget everything about himself and become Nathan, and changes his appearance to look like Nathan. Noah, Angela, and Matt agree to keep Nathan's death a secret. Volume Four ends with Claire, Noah, Angela, Peter, 'Nathan', Mohinder, Matt, Ando, and a recovered Hiro all gathered around the burning corpse of Sylar, though actually the body of the morphed James Martin. The group then proceeds their separate ways, and 'Nathan' confirms the President has indeed shut down Building 26, and the funds transferred so that Angela and Noah can start up their own company which Noah favorably wants to call "The Company".
Volume Five: Redemption begins six weeks later with a former Building 26 agent arriving home to find his sink flooded. As water spreads on the floor, it solidifies, turning into Tracy Strauss. She then proceeds to drown the man, and she implies that she has done so to several others. Meanwhile, Angela meets "Nathan" at his office. "Nathan" is bothered by a clock that is ticking in the background and observes that it is running fast by a minute and a half, cryptically revealing that even though Nathan's persona is in control, Sylar's intuitive aptitude still remains intact.
Overnight figures shows that the episode attracted 6.38 million viewers, with an average rating of 3.0 in the 18-34 demographics.
This episode received mixed reviews by critics, especially in regards to the death of Nathan and Sylar's subsequent transformation into him.
Positive reviews include the Los Angeles Times which said that the episode was "the best ending so far" and had "edge-of-your-seat anticipation." Robert Canning of IGN said the ending was "quite possibly the coolest twist the series has ever given us" and gave the episode 8.3 out of 10.
Entertainment Weekly's Marc Bernardin praised the twist, as well as Angela's anguish over finding Nathan's body, but blasted the show for not showing the fight between Peter, Nathan, and Sylar.
Negative reviews include the Boston Herald, which said that Heroes ". . . makes Deal or No Deal look brilliant." and the New York Post who called the Sylar/Nathan twist "probably one of the worst decisions Heroes has ever made. And that's saying a lot!"
The A.V. Club brought together the three reviewers of Heroes' third season, Steve Heisler, Josh Modell and Sean O'Neal and included a live blog in the review. They rated this episode a D-, calling the show "Still stupid after all these hour."