The Mole's Jon Kelley by Bob D'Amico/ABC The Mole's Jon Kelley by Bob D'Amico/ABC

After a four-year absence, The Mole returns to ABC Monday night (10 pm/ET) where contestants complete a grueling series of physical and mental missions. This is ultimate teamwork: the missions have to be completed together in order to build up cash amounts that are eventually won by the winner.

But beware the Mole - a saboteur and one of the 20 contestants whose mission it is to prevent the group from winning the cash. All the while, the players try to figure out which one of them is the Mole through a series of quizzes.

At the end of each episode, the players are quizzed about the person they think is the mole (example: on the first night, where was the Mole assigned to sleep?) Score the lowest, and you face "execution." The player who survives all the executions over ten weeks wins the cash that has been accumulated by the group - up to $500,000.

"This is like a mystery. A Whodunit," says executive producer Clay Newbill. "The list of clues players must find is like something out of a mystery novel."

Former Extra host Jon Kelley hosts this season's series of mysteries. Wanna know who's the Mole? Don't ask him. "I have no idea," he says. "And that's the way I like it. It allows me to play along. Sometimes I think I'm absolutely sure of who it is and then it blows up in my face."

After two seasons of Celebrity Mole in 2003 and 2004 (before the franchise took a four-year hiatus from TV), the series is back with civilian contestants. Newbill says advanced technology has allowed a more high-tech and entertaining presentation. "I like to call this 'Bionic Mole' - bigger, stronger, faster."

Contestants this season are dropped off in Los Angeles, Chile (yes, you read that right) and among the missions is to scale a huge waterfall. Unlike Survivor, where contestants eat whatever they can find and sleep outside, players on The Mole have had the luxury of staying in high-class hotels. There will be less of that this season. Says Newbill: "While there is still some of that glamour of hotels and fine wine, the missions sometimes call for the contestants to be out all night in sub-freezing temperatures. Like traveling through the Andes. Or having to scale the Salto Del Laja Falls [on Monday's premiere]. It's not easy for them."

It takes a little more than just being smarter than the average bear to have a shot at winning. "In the past, we've had contestants who were doctors and lawyers," Newbill says. "Those are occupations that require a lot of book smarts. That won't necessarily help you on The Mole. You must be very perceptive and have a very good sense of strategy. You've got to have good gut instinct and be able to adapt to different situations."

Also, this year, the show has a very strong online presence allowing viewers to play along as if they were on the show. "People can take the same quiz online as the contestants on the show," says Kelley. "Plus, there will be three or four clues on the web site pointing them to the identity of the Mole." - J.R. Whalen