The following contains MAJOR spoilers for the CBS show, "Threshold."

The CBS Earth-bound science-fiction series "Threshold" has added two new recurring characters, according to SciFi Wire.

Catherine Bell, who portrayed Lt. Col. Sarah "Mac" Mackenzie on the CBS show "JAG," will portray a genetic engineer who becomes a part of the Red Team, according to Brannon Braga, "Threshold" co-creator and executive producer. Bell will also appear on the SciFi Channel miniseries "The Triangle" in December.

A second character, the previously unseen fiance of Lucas Pegg, will also join the cast. "She's going to become a recurring character," Braga said. "She's cool and pretty. She's actually a research physician at the National Institutes of Health in Bethesda, Md., and Lucas is going to go through a very traumatic experience where, having watched that alien videotape in the pilot, he starts to unravel.

"And she's going to come into the story. They can't tell her what's going on, and she's not allowed to see her future husband," he said. "She's going to become a source of conflict for Molly Caffrey, leader of the Red Team."

On Nov. 22, the show comes back to the CBS weekly schedule in a new Tuesday, 10 p.m. ET/PT time period. In order to help new audience members understand what has happened previously, "we cut together a really cool trailer, like a minute-long 'saga sell,' to bring people in and get them familiar with the show immediately," Braga said. "It's almost like a music-video-type montage saying 'Here's Threshold.' That will actually premiere Tuesday night right before the episode begins."

There are some surprises in coming weeks, including the return of Gunneson, the human infected by the aliens during the show's opening episodes. According to Braga, he's re-appear "in a very, very unexpected way when he appears in Molly's nightmare."

The following week, on Nov. 29, the infected prisoners attempt to break out of Threshold headquarters in "The Crossing."

Want more information? Fans can watch previous episodes at CBS.com.