The future returns to haunt the past this week on the highly anticipated second season of "The 4400 (search)."

The USA Network (search) series, which in just six episodes last summer became the breakout cable drama of the season, is finally back on Sunday at 9 p.m..

"It's a show that has sci-fi elements, but also relatable, human stories and characters that have problems that the average viewer can get behind," says Ira Steven Behr (search), the show's executive producer and one of its main writers.

"The 4400" of the title refers to the number of people who mysteriously disappeared over the course of about 50 years only to return to Earth all together on one night transported on a comet that turns into a big ball of light just before it lands.

None has aged a day since they were taken.

After spending months in a government quarantine, the 4400 are released back into the world. Many learn they have acquired superhuman powers and don't understand why. Some are alone, without relatives or friends because they've either died years before or moved on.

Of the 4,400, each episode has focused on the storylines of a handful of the returnees.

Among the important players are:

* Richard and Lily (played by Mahershalalhashbaz Ali and Laura Allen), an interracial couple from different decades who met in quarantine and now have Isabelle, a mysterious baby.

* a spooky little girl with ESP named Maia.

* and a super-rich businessman who has appointed himself the spokesman for the 4400 and now started a quasi-religion around them.

Despite its record-shattering ratings, "The 4400" almost didn't come back this year because of angry network politics.

A dispute over rerun rights was eventually settled and Behr was given the green light to start working on new episodes.

"Once the smoke cleared and we were told the show would be back, it was just a matter of figuring out how big a hole they had dug for us," says Behr who was worried that there would not be enough time to write season two.

Most of the ideas for new season, he says, were thought up well before the show was renewed, over "pinball games" and walks on the Warner Bros. lot when he was working on another show.