Paralleling the Warren Jeffs and David Koresh cases, the episode features Federal Bureau of Investigation (FBI) agents and mathematicians attempting to locate and arrest the leader of a polygamist cult in which members marry young girls.
California Bureau of Investigation (CBI) Agent Rachael Willions (Teri Polo) tells FBI Special Agent Don Eppes (Rob Morrow) that the girl is Josephine Kirtland (Alexandra Krosney), the 73rd wife of Abner Stone (W. Earl Brown), the leader of a polygamist cult called the Apostolic Saints.
Charlie Eppes (David Krumholtz), Don's brother and an FBI math consultant, and Amita Ramanujan (Navi Rawat), Charlie's girlfriend and colleague, receive Don's call for assistance while traveling to Stanford University to attend a mathematics conference.
Emmanueline expresses her displeasure of Josephine's preference of dating a young man who was no longer a part of the cult, Lee Brady (John Patrick Amedori), to being Stone's wife.
Josephine leaves the hospital with Lee and calls the FBI 45 minutes later, reporting that her mother is missing and there is blood in the kitchen.
Charlie and Amita also realize that, since she is not biologically related to him, Stone's next potential wife is Emmanueline Kirtland, Josephine's mother and, as the analysis demonstrates, half-sister.
A fellow cult member fatally shoots a California Highway Patrol officer who had stopped the van they are traveling in for a traffic violation.
Stone instead walks out of the building with Emmanueline and sets fire to the house, killing the remaining people inside.
At the house, Alan and Charlie discuss the fact that Stone took advantage of people's spiritual searches to further his agenda.
Series writer/producer Julie Hébert decided to base a script on the fundamentalist polygamous groups and cults found in 12 states.
To hide series regular Diane Farr's pregnancy, she used a folder and a bag made from a material that was not supposed to make a sound when folding it.
Using a bicycle and a shotgun, Tom Bellissimo, Numb3rs' special effects supervisor, built the booby trap for the explosion at the trailer.
Christy Somner, California's first female pyrotechnician, assisted Bellissimo, and stunt coordinator Jim Vickers pulled the door to the trailer once filming was underway.
To create the illusion that Stone and Emmanueline were closer to the house than they were, the crew used a long-lens camera to shoot the explosion.
[5] Jeffrey Robinson, a reviewer for DVD Talk, highlighted "Nine Wives" as an excellent episode, stating that it "revisits a somewhat common cult theme to crime-dramas".