Castaways scale new heights as they battle for a guaranteed spot in the Final Four. Meanwhile, friends become enemies when one castaway overhears plans for her eviction, and Tony comes up with a strategy for his special Immunity Idol.

The 500th Episode of "American Idol" airs tonight and the Top 3 final contestants compete tonight to move on in the competition to become the next "American Idol".

Sue is determined to win herself a car and enters Ehlert Motors 'Hands on a Hard Body' contest, in which the last person whose hands never leave the car wins. Meanwhile, Mike and his perpetually down-on-his-luck brother Rusty, find time to bond again when they take a road trip to Chicago with Brick to attend his Spelling Bee, and Frankie has to travel to Axl's college dorm to help him locate a missing desk or risk losing her $200 deposit.

In a special clip episode, Mel and Joe meet with a counselor to discuss their relationship. As they look back on their years together, they quickly decide that honesty is not the best policy.

United by their desire to take the Patriots down, Neville and Monroe form an uneasy alliance. As Rachel comes face-to-face with the nano-tech while searching for Aaron, things don't go according to plan for Miles, Charlie and Gene when they try to steal the Patriots' supply of mustard gas.

Slade moves forward with his plan to kill one more person in Oliver's life. While Oliver has fought all year to be more than the killer he once was, when Slade kidnaps someone close to Oliver's heart, Oliver is pushed to the edge and realizes sometimes it takes doing the unthinkable to stop the monster. Meanwhile, Diggle takes on Amanda Waller with a little help from some friends, and Thea turns to Roy in her time of need.

When Tessa joins a knitting circle, George is a little surprised by the age gap between Tessa and her new friends. Still reeling from his one-night stand, George decides to put pen to paper and writes a song dedicated to his muse. Meanwhile, newlyweds Malik and Lisa can't seem to get along.

Ben, Danny, and Riley take stock of their lives when they review their fifth-grade time capsules.

The bartenders have spoken and it's last call at Mix. Bar tabs aren't the only things that need to be closed as Tom finds himself bonding with Liv while she tries to help him take home Maya. But in the process, Liv and Tom can't help but realize they might actually be meant for each other instead. Bruce starts to panic when he realizes Jessica is probably going to go home with Dominic, so he sets out to find a backup girl he can take home but learns some things aren't always what they appear.

Clarke and Finn attempt to broker peace with the Grounders but all hell breaks loose when Bellamy, Jasper and Raven show up armed and ready for battle. Octavia and Lincoln grow closer. Meanwhile, tragedy strikes during the Unity Day celebration on the Ark.

Frank and Dave's road trip through Florida gets stranger at every turn, from a creepy collection of kitsch to a tugboat that's home to a Captain and his unusual pet. And back in Iowa, Mike readies the new shop for its Grand Opening.

Colditz Castle, a notorious prisoner of war camp in Nazi Germany, was supposed to be escape-proof. But in the dark days at the end of World War II, a group of British officers dreamt up the ultimate escape plan: in a secret attic workshop, they constructed a two-man glider out of bed sheets and floorboards. Their plan was to fly to freedom from the roof of the castle, but the war ended before they could put it to the test. Now a crack team of aero engineers and carpenters rebuild the glider in the same attic using the same materials, and they'll do something the prisoners never got a chance to try: use a bathtub full of concrete to catapult the glider off the roof of the castle. As the hair-raising launch 90 feet up draws near, the program explores the Colditz legend and exposes the secrets of other ingenious and audacious escapes. Then, after a 70-year wait, the team finally finds out if the legendary glider plan would have succeeded.

The BAU continues its murder investigation in Texas, and clues uncover a deep web of corruption that could be the motive for the killings. Meanwhile, as one team member's life hangs in the balance, another concerned BAU member must face a sad secret from the past, and Garcia is thrust into action to save a colleague.

Under the guidance of Lieutenant Murphy, Sergeant Benson and the SVU take an active approach to catching sex offenders - they target Simon Wilkes, a well-regarded photographer with a secret life. An undercover investigation finds his graphic fantasies may have crossed the line into reality, at a child's expense. But the case becomes impossible when no evidence of a victim is found.

Mitch and Cam's big day is finally here and nothing can ruin it, until nothing turns into a whole lot of somethings and puts wedding planner extraordinaire Pepper Saltzman to the test. Meanwhile, Jay and Gloria host the Tuckers, Phil squeezes in an eye procedure before the festivities and Claire embraces her role as "best woman".

Nev and Max respond to a call from Antwane's cousin Carmen. She is worried that Antwane's 3 year relationship with Tony isn't what it seems after he met him a telephone chat line.

As Antonio's life is now in question, Voight and Platt open up about their pasts. Jin is caught while tinkering with Voight's computer and uses the only scapegoat possible to keep him in the clear. At the same time with Charlie back in town Lindsay realizes she's going to have to come clean about a few things. Halstead finally gets answers he's been wanting about Voight's and Olinsky's past.

Corey Anderson of Team Edgar fights Josh Clark.

Melanie decides to use an illness so that she can get her hands on some tickets for a sold-out concert.

As Will Lexington's album climbs the chart with the help of Jeff Fordham's deep pockets, Rayna enlists Teddy's help to plan a huge, free concert at LP Field to draw attention to her Highway 65 debut. She will perform with Luke Wheeler and duet with Juliette before thousands of fans. Zoey, Avery and Gunnar rock out at a benefit for Deacon's favorite charity, Sober House, and Avery plans to serenade Juliette with a song he wrote for her. But when he attempts to sing it, he doesn't understand why she is not present. And Scarlett makes a decision about her future in Music City

Tonight "The Soup" goes on the road for an episode from New York City with special guest stars Andy Cohen & Willie Geist.

With Larrick closing in, Elizabeth rushes to exfiltrate Jared while Philip readies Fred for a crucial mission. Arkady finally plays his hand, forcing Stan to make an impossible choice.

Jim stops drinking in solidarity with Steve and starts to suffer from panic attacks. Through a misunderstanding, Jim ends up at a married ex-girlfriend's house for a costume party.

In an effort to move into a new phase of their lives, Boyce and Lolli decide to sell their house and move into a luxury condo. After kicking their family out of the condo, they both question whether they did the right thing.

Jim deals with the fall out of being shot by a heckler and considers quitting comedy. Billy goes to a video game tournament.

Blondie

Keri Russell

Tonight guests are actress Maya Rudolph and actor Robert Duvall. Musical guest will be English singer Lily Allen.

Also Tonight Show Audience Suggestion Box (appearance by Two Really Fun Men, Lance Bass; singing "Big Mouth Lance Bass"); Maya and Jimmy invent new characters; Lily Allen performed "Hard Out Here".

Barbara Walters, Elle Fanning, Randy Houser

3 celebrity contestants compete to determine who has the funniest take on the day's pop culture.

Seth was joined by Tina Fey and Matthew Rhys, plus music from The Wild Feathers.

Carrie Ann Inaba, Brad Trackman, Keb' Mo'