"The Mentalist" returned from its hiatus with a murder investigation that took the team to the Texas/Mexico border.

In "Black Helicopters," the FBI team investigates the death of Edith Firlock, a federal attorney whose body is found on the Mexican border. It's discovered that she was fatally shot in another location, then her body was dumped at the border. Jane (Simon Baker) suspects that she was on an undercover mission.

Jane finds that the victim was killed in Texas, then the body was dumped in Mexico using an underground tunnel that is used to connect the borders. The owner of the land where the tunnel is located says he found Edith's body on his land, but moved the body out of fear that he would be implicated. The victim was actually going to Gentry, Texas.

Lisbon (Robin Tunney) finds that the victim was looking at pictures of a farmer's market in Gentry before she left.

At the same time, Lisbon is trying to figure out who tapped the team's phones, and who killed Ardilles. Jane suggests that they ask J.J. LaRoche (Pruitt Taylor Vince), since he owes Jane a favor.

Jane and Fisher (Emily Swallow) then arrive at the farmer's market, and Jane is eventually invited to spend some time on the farmers' land.

Meanwhile, Van Pelt (Amanda Righetti) and Rigsby (Owain Yeoman) talk with LaRoche, who agrees to get a warrant to search an area that may lead to Ardilles' killer.

In Texas, Jane is sure that Edith went to Gentry to meet with someone from the farm, which is when she was killed.

It turns out that her killer is Rachel, a woman who is a suspect in an eco-terrorism bombing on the Canadian border. Edith's defense fund represented her until she skipped bail. Now, 10 years later, she appeared to tell Rachel to turn herself in, which prompted Rachel to murder her.

Back in California, LaRoche and Rigsby search the area, but whoever killed Ardilles set a trap that quickly kills LaRoche.

In the next episode, "Grey Water," "Jane and Fischer investigate a murder at an oil fracking site, while Rigsby and Van Pelt travel to Austin to help investigate suspects in the string of attacks on former CBI members."

Watch the promo for "Grey Water" below, which airs Sunday at 10 p.m. EST on CBS.