TV dramas used to seem easy to plan, to make and to watch.

Simple plots assured that bad guys were caught at the end of each hour. Simple viewers were pleased.

That's changed lately, though. A prime example is "Day Break," which debuts tonight on ABC, borrowing the "Lost" slot for three months.

"It's head-bangingly complicated," said producer Jeffrey Bell.

He was talking about planning this show, in which police Detective Brett Hopper (Taye Diggs) keeps waking up to the same bad day. Hopper keeps trying to rework the day and to redeem himself.

Then again, Bell could have been describing the complications of watching the show or of acting in it. "The challenge is to wake up every day and lose the information," said co-star Victoria Pratt.

Actors usually build a character's depth as the show goes along. Not this time, though. Only Hopper learns from anything that happened previously.

"He's the only thing that carries over from day to day," Bell said. "If he gets hurt, he's hurt the next day." And if he gets killed, the show is over; that part has no do-over.

The other characters, however, must start fresh each day, bewildered by Hopper's obsession with changing things.

There is Rita Shelton, his lover. "I was sort of the sunshine of his life, the safe place," said Moon Bloodgood, who plays her.

There is Andrea Battle (Pratt), a tough detective who is his police partner. "I'm a good cop who did all the wrong things for all the right reasons," said Pratt.

There's his sister Jennifer Mathis (Meta Golding). And a key crook-turned-informant, Damien Ortiz (Ramon Rodriguez). And the looming Chad Shelton (Adam Baldwin) who's been Rita's husband and Hopper's police partner.

These actors show up each day, pretending they know nothing from previous episodes. It's challenging, but not compared with other fantasy fiction. "I don't have to suspend gravity," Pratt said.

She used to do that. A former star athlete in Canada, Pratt was hired for exotic roles. She was Cyane in two "Xena" episodes, Sarge in "Cleopatra 2525," Shalimar Fox in "Mutant X."

This time, no gravity-defying powers are required. Instead, it's the internal challenge of one character forever trying to do things over and make new choices.

As Diggs explains it: "Do you remember those books, 'Choose Your Own Adventure?' ... We all get to figure it out together."

Some people are trying to frame him and to hurt everyone around him. He keeps trying to prevent it; solving one thing, however, can make the others much worse.

All of that will be resolved, promises creator Paul Zbyszewski. "In 13 episodes, we have a payoff, a big payoff. And the following season would be another day."