"Days of Our Lives" actress Deidre Hall was as shocked as anyone to learn she has been killing her co-workers.

last fall, a serial killer on the NBC soap (weekdays at 1 p.m. on WHDH, Ch. 7) has murdered eight characters, many of whom have been favorites for decades. The killer was recently revealed to be Dr. Marlena Evans - Hall's character - one of the show's longtime heroines.

The story line was prompted by declining ratings and rising production costs. To win the show a two-year renewal, executive producer Ken Corday made a deal with NBC: He'd trim the cast by a third - hence the appearance of a masked killer.

The story line has been a boon for the show's ratings, stunning viewers and cast members alike.

"I was surprised," Hall said in a recent interview. "I thought it might be me, but I thought there might be another explanation."

The actress was hoping the script would leave an escape for Marlena. Through the years, Marlena has done a few vile things, but there were extenuating circumstances typical of a soap: an evil twin and, in one case, demonic possession.

This time, there was none of that to fall back on.

For months, even the show's cast did not know the identity of the killer.

Corday called Hall into his office to break the news.

"He just said, `Honey, it's you,' " Hall recalled.

The killings will continue through the spring, according to the network, and not even the cast knows who will be the next to be axed - figuratively and literally. Corday approaches each "victim" in advance to break the news.

"It's not comfortable around here," Corday has said of the mood around the set. "The cast is walking on its tip-toes. They don't look for a hug when they see me coming."

The killings have been especially graphic: a brick to the head, bludgeonings and stabbings. One character was knifed and then stuffed in a pinata.

"I will be interested to see how they will resurrect Marlena after all this evil," Hall said.

Before the identity was revealed in the script, a stunt actor was used to film the killer's scenes, shrouding the murderer in mystery to everyone but Corday and head writer James C. Reilly, who is spinning the story line.

Now that Evans has been revealed to the viewing audience, Hall has been playing out the onscreen crimes. She says playing such brutality has been difficult.

Despite her misgivings over the graphic nature of the story, Hall says she has faith in Reilly's writing skills. Somehow, someway, he'll find a way to redeem Marlena.

"I'm not especially concerned about where she is going," Hall said. "I just don't know where it is, exactly."

In the real world, when killers are caught, they are generally found guilty and shipped off to prison or given the death sentence. But in the soaps, if killers turn out to be popular characters, they usually find redemption and are spared punishment.

What if this isn't the case with Marlena?

If the show's heroine is made to pay for her crimes, it could spell the end to one of daytime's most durable characters. Marlena's punishment could coincide with Hall's contract negotiations, coming in August.

Hall has been with "Days" since 1976 and remained in a front-burner story line for most of that time.

"We've had no conversation about (contract) renewal," Hall said. "But, listen, in this business you're lucky to have a job. In this climate, anyone here would be crazy to assume anything as far as their job. The show can go on without any one person. That's the nature of the business."