The team finds themselves in a race against time when a terrorist group threatens to detonate a "dirty bomb" in the D.C. area.

The judges continue their quest to find the next singing superstar in the Mile High City with returning guest judge Victoria Beckham. Don't miss the auditions that everyone will be talking about the next day.

This week, contestants are surprised by the return of the blue and yellow teams, who were sent home after the first challenge of the season. Now they're back, 30 days later, to weigh in and try to earn a spot back on the ranch. Then a vigorous football challenge tests everyone's stamina, except for one player sidelined with medical issues, and provides immunity for the winner - but a big disadvantage for the losing team. Later, after another elimination round sends a player home, host Alison Sweeney surprises the contestants with exciting news.

Perched atop a mountain crest, mysteriously abandoned more than four centuries ago, Machu Picchu is the most famous archeological ruin in the Western Hemisphere and an iconic symbol of the power and engineering prowess of the Inca. In the years since Machu Picchu was discovered by Hiram Bingham in 1911, there have been countless theories about this "Lost City of the Incas", yet it remains an enigma. Why did the Incas build it on such an inaccessible site? Who lived among its stone buildings, farmed its emerald green terraces, and drank from its sophisticated aqueduct system? NOVA joins a new generation of archeologists as they probe areas of Machu Picchu that haven't been touched since the time of the Incas. See what they discover when they unearth burials of the people who built the sacred site.

A parallel universe, in which the crash never happened, is revealed as an aftermath of the bomb's detonation. Meanwhile, Sawyer blames Jack for the loss of Juliet and the true identity of the monster is revealed.

After Gordon works with a New Jersey restaurant's employees to make changes, the skeptical owner thinks it may be best to shut down the business.

Mike creates some concrete counter-tops and fire pits in Moss Landing, California and then reminisces about the scariest job he's ever done.

A crime scene poses a national security risk when the LA team discovers the location was used to create a deadly toxin which is now missing.

Coming Soon...

Jack, Sawyer, Kate, Miles and Hurley, struggling to save Sayid, face an ancient secret. Meanwhile, a fake Lock exits the chamber to everyone's awe.

Tensions are high as Peter's appeal trial begins and Alicia defends a wealthy client in civil court whose innocence she doubts, even after he's found not guilty in criminal court of murdering his wife. Meanwhile, Diane decides to take precautions when a felon she successfully prosecuted is about to be released from prison.

When Neal discovers illegal trafficking in organs, he and Peter try to find a way to expose the ringleader.

Alex finds himself in a much desired stress-free situation after a demotion makes him the third-string quarterback. However, after being forced to hang out with the special teams, he is desperate to reclaim his lost position.

Brian Williams

Tonight Stephen welcomes the former New York Governor and current columnist for Slate.com, Eliot Spitzer.

John Travolta, Ben Harper & Relentless7

Ric wants to get rid of Thandie. He tries to prevent her being considered for a full time post, but realises he would do

For centuries scientists have been attempting to come up with an elixir of youth. Now remarkable discoveries are suggesting that aging is something flexible that can ultimately be manipulated. Horizon meets the scientists who are attempting to piece together why we age and more vitally for all of us, what we can do to prevent it. But which theory will prevail? Does the 95-year-old woman who smokes two packets of cigarettes a day hold the clue? Do blueberries really delay signs of aging or is it more a question of attitude? Does the real key to controlling how we age lie with a five-year-old boy with an extraordinary aging disease or with a self-experimenting Harvard professor? Could one of these breakthroughs really see our lives extend past 120 years?